Flights from FLR to SEA, which to book

The answer to your question depends to a great extent on whether you are talking about a ticket booked as a single itinerary, or two (or more) individual tickets. On a single ticket, if you mis-connect, the airline will get you home. That might take a while, depending on schedule and seat availability, but getting you home is the airline's problem, not yours. If you are on separate tickets, and you miss a flight, the airline has no responsibility to help you, and getting home is your problem (potentially at great cost), not theirs.

LHR is a huge, sometimes messy airport, and personally I try to avoid it if I can. If connecting there I allow plenty of time. If trying to "connect" on two separate tickets, allow LOTS of time (I'd allow way more than 1 hr 20 minutes and if you are trying to catch a flight from LHR to SEA - which could be financially debilitating if you miss your flight and have to buy a same-day ticket to get home - a lot more...if on separate tickets, I'd be nervous even with 2 hr 40 min to catch the flight....you should look at the cost of a same-day, walk-up ticket from LHR to SEA to help you assess the risk and consequences of missing the flight).

If you are talking about a singe ticket all the way, then the short (1 hr 20 min) connection looks like it might be do-able (because they would try hard to put you on the next available flight).

One other thing to consider: Flight schedules change (a lot). Somethings they just jiggle by a few minutes either way, sometimes they move more, so connection times can shrink or grow. For a flight 9 months form now, at least one of your proposed flights will very likely shift at least a little, impacting connection times. Again, not really your problem (probably) if booked on one ticket, but if separate tickets definitely your problem if a connection time shrinks significantly. IME British Airways has more schedule shuffles than most airlines (British Airways is American Airlines' primary partner - check to see if any of the airplanes you are booking is one of theirs; the intra-Europe flight almost certainly is). Having had British Airways flights with multiple schedule changes and last minute flight cancellations (leaving me with no way to get there/home) I would look for even more flexibility/resiliency in my flights if any legs were on BA (again, more of a worry if on separate tickets, if on a single ticket, I would be less paranoid).

thanks. unfortunately, flying to LHR would be just about my only choice from FLR...sounds like I should go with the 8h layover...sadly

I didn't say that LHR is necessarily a problem. LHR may be fine for you. It depends.

You need to be clear about whether what you are proposing is on a single ticket or separate ticket - that's quite critical and can make a big difference.

If you are a single ticket, all (well, most) of your worries go away. On a single ticket, if you like the one-stop itinerary, I'd book the 1 hr 20 min LHR connection (American/British Airways wouldn't sell you a ticket with that connectin time if they didn't think you had a chance of making it). 1 hr 20 min at LHR is tighter than I'd like, but it's possible - and as you have seen, there's a second flight 1 hr 20 minutes later they can probably get you on. But if you are booking separate tickets, all bets are off (and if it were me, then I'd opt for the 8 hour connection, but I have a low tolerance for stress....to see how "bad" it would be in that case, you really should look at what it costs to buy a ticket from LHR to SEA today, because that's a reasonable predictor of what it would cost you if you miss the flight; go ahead and check that out, it's the only way to know how risky or not it is to you; then consider what spending 8 hours in that airport would save you or how much you would be willing to pay to skip that experience). I've spent 8 hours in an airport before (though not in LHR) and it can get old quickly, but sometimes it's the right choice (at least for me).

it would be a single ticket

I've made similar connections at LHR and I would avoid the 8 hour layover and take the 2 hr 40 min. connection - that should be plenty of time to make the connection even if the first flight is a little bit late. I've easily made connections at LHR with a 2 hour layover. The nonstop to SEA is definitely worth that LHR layover, IMHO. Also remember that they start boarding about 45-50 minutes before the scheduled takeoff.

thanks. As long as I have your attention, how far out (or close) should I be purchasing. I'm thinking it's too early at the moment (9 months away); in your experiences is there an 'optimum' window?? (I've been checking everyday).

That changes everything (well, almost everything).

On a single ticket, I'd take that 1 hr 20 min connection. It's a "legal" connection (the airlines are betting you can make it). If you have only carry-on bags, you will probably make it without breaking sweat (and since you are on the way home, if your checked bag doesn't make the connection it's not a major disaster, they'll deliver it the next day). Best if you can be seated near the front of the plane so you can exit reasonably quickly, but probably no need for drama or heroic sprints through the airport - just be direct and efficient.

Do keep an eye on your flight schedule between now and September (be proactive about this as airlines sometimes fail to notify you of a schedule change - I check my flights once a month, more often in the last 30 days). Worst case, if you miss that 1 hr 20 min connection, they will try hard to get you home on the next flight, and there are enough flights going that can get you there you would almost certainly get back the same day as planned.

If you're on a single ticket, you can move "missing my connection in LHR" way down on your Prioritized List Of Things To Worry About.
Enjoy your trip to Italy.

how far out (or close) should I be purchasing. I'm thinking it's too early at the moment (9 months away); in your experiences is there an 'optimum' window?? (I've been checking everyday).

This is a question that's not possible to answer, as it's impossible to predict fluctuations in flight prices in advance.

If you've been checking every day for a while, you know that prices typically fluctuate. There is no rhyme or reason to price changes (they are dictated by computers). What is almost always true is that prices go up (and then WAY up) as the flight date approaches. Otherwise, it's all a roll of the dice, there is no "optimum window." Personally, I do not think 9 months out is "too early" at all. I book most flights 11 months out, but that's me.

The general advice seems to be: watch prices for a while to get a sense of the range they move within, and when you see a price you are comfortable with, grab the ticket and stop obsessing over saving a few bucks. Peace of mind is worth something, so if there's a price you can live with, go with that and be done with it.

I know nothing about American Airlines, but could you fly to Paris, Munich, Frankfurt or Amsterdam from FLR instead of to London?
Then home from one of those?
Or.. go to Rome , Milan or Naples by train from Florence, stay one night, fly home from there.
Lots of options other than London.
If choosing your London idea, the 2:40 connection will be fine, if both flights are booked on the one ticket.

Yes, there are plenty of other ways to get home to Seattle without going through LHR, but the OP appears to want to use credits they have with American Airlines, so that will limit their choices. American Airlines does not have any intra-Europe flights of their own, so if booking through AA you will be on a partner airline until you hop the Atlantic, and for AA, that usually always means British Airways for the intra-Europe flight, which means you're going through LHR.

As noted above, nothing really wrong with LHR (it's not my favorite airport and has some other shortcomings for me, but it's functional and I would not avoid it like the plague if it made sense otherwise). The OP's plan through LHR seems perfectly reasonable to me.

Worth noting: getting home to Seattle when you are starting from a secondary airport in Europe is not easily done with just a single connection, and it can often take more than a day (if you have a connection in the eastern US, it's often too late to catch an onward connection to SEA due to flight schedules, requiring an overnight on the east coast). With just a single stop and departing from FLR (an airport with no nonstop flights beyond Europe, as best I can tell) and getting home on a non-stop from Europe to the US west coast - that's even harder. So the OP's plan looks like a choice I might make given their constraints.

Though it's true that there are other departure airports in Italy that could work - look at Rome (American flies from FCO to multiple US destinations) or Milan (only JFK I think). But most of those options will only get you to a US hub, and then leave you stuck overnight in that city waiting for an early morning flight to Seattle (I did not search those options exhaustively today, but it's what I'm used to seeing when trying to get home from Europe to Seattle in one day...options can be surprisingly limited, given the schedules for domestic US connections). The LHR option looks like what I would probably end up picking. Choose the 1 hr 20 min connection if you're in a hurry and don't mind a small risk, or pick the 2 hr 40 min connection and you can relax.

thanks everyone. very helpful.

How early in the morning is the flight for the 2:40 connection?

Assuming FLR means Florence, that is most likely the problem. Florence has a very small airport and your options will be limited. Looking at flights from Milan will give you a lot more option. Even Pisa will probably be a better choice.

it leaves FLR at 12:25pm; the Seattle bound flight leaves LHR at 4:30pm

Is going to Rome and flying from there something you would consider?

If so, there are several flights from Rome that land in the US and then one more flight to Seattle.

Will you be in coach or something better? When I went through LHR ( precovid) biz class passengers had 'express lanes' to use getting from one gate to the next ( e.g., separate uncrowded escalators) No idea if that still exists to help expedite a transfer.

If you do select the 1 hr 20 min itinerary, I suggest using the restroom on the 1st flight before it lands so you don't have to 'detour' while making your way through the terminal. The 80 minutes is enough time but there is no margin for side trips.

Plug in you possible flights to see what the process is--
https://www.heathrow.com/connecting-flights

yes, could go thru Rome, though adds time to the journey (florence to rome, rome to chicago, chicago to seattle). Alas, There's just no easy way to get back to the 'left' coast