2025 Customs experiences in Heathrow

You mean immigration, right? Customs is more or less a formality assuming you go through
the "nothing to declare" portal.

Customs should be fairly quick if 1) the e-gates are open at passport control 2) you have a
biometric passport that allows you to use the e-gates. It really has nothing to do with the
specific terminal. It can be breezy easy or a mob scene depending on the e-gate status
and the # of incoming flights.

Presumably you are asking to try and decide how to schedule your train. So you'll also need
to take into account how you are getting to Paddington or whichever station you plan to get to.

If you search the subforum you will see comments about taking the bus from Heathrow to Bath
instead of the train from Paddington. That cuts out one segment of the journey.

Yes, immigration is what I meant. Trying to decide whether or not to buy train tickets now, not knowing how long it might take.

First, one correction, American Airlines is at Terminal 3.

I fly AA into Heahtrow quite a bit. I did it three weeks ago. Nothing has changed. This past time I was lucky and no other flights were arriving when I went through. The walk from my gate to the egates was about 10 minutes. Time to get through the egates was less than a minute. Then downstairs to baggage claim (which I don't bother with as I only have carry on) and out the door.

The problem, of course, is whether or not your plane is on time. You have no way of knowing this and neither do we. The same goes for the number of arrivals at T3 when your plane arrives. The last part is whether or not your passport will work in the egates. Older passports sometimes give a problem. (But not to worry, if that happens you are directed to a side desk where an officer will admit you. It's faster than the regular line.)

What time are you arriving?

Of course, there are numerous options to get from Heathrow to Bath....local train (Elizabeth Line or Heathrow Express to Paddington) then GWR train to Bath; Railair Coach to Reading and then train to Bath (same train from Paddington stops here); direct coach from Heathrow to Bath.

And don't forget to get an ETA.

Same experience as Frank - two weeks ago. 10 - 15 minute walk from gate to the E-immigration machines. Place passport in machine, have your picture taken, and then walk through and you’re done. I had no baggage to claim - walked through customs area and out.

The bottom line is that it doesn't matter how long it takes to get through immigration when heading to Bath.
The trains are fundamentally long distance commuter trains.

If you buy the cheapest possible Advance Ticket you are tied to that train, so are either clock watching or have too much time in hand. You are on a multi thousand $ holiday. Differences in train fares are miniscule in that context.

Quite simply arrive when you do and take the first train to Paddington then the first train (they run every half hour) from Paddington to Bath.

Or by bus, two companies run the route - National Express and Flixbus. Note down their times beforehand. If you happen to be through immigration soon before a bus departure, just buy a ticket for whichever company runs first on your phone.
Flixbus are the new kid on the block so are too new to be in the RS books.

If not go for the train option. If you don't want to deal with a clerk or machine at Paddington to buy the train ticket again do it on your phone. Same prices.