Which Route from Dalwhinnie to Edinburgh?

A9 - about 1 1/2 hours. Is this a nice scenic ride? It looks to be mostly “highway.”

I see you have also posted this on Trip Advisor, and you haven't responded to the very good answer of adding in stops at Pitlochry and Dunkeld. House of Bruar (the 'Harrods of the North' is more debatable but there is a very nice short scenic walk you can do from their parking lot).

That is a wildly optimistic timing. It is highway, and if you go onto the M90 at Perth is 2 hours 3 minutes according to AA route planners. Stay on the A9 into Edinburgh and it adds another 30 minutes. I really would not like to see anyone trying to do that journey in your timing. Not saying it's impossible (we do have several drivers like that on this forum) but it is aggressive driving and (if not actually stopped by a traffic policeman) you'll be getting speeding tickets in the mail afterwards. I don't want to be on the same road as you.

Scenic Option - about 2 hrs 15 min - General Wade’s Military Road along the Tay National Park to the B846 and crossing the River Tummel then turning to drive along the River Lyon and then the A827 along the north side of Loch Tay to the A85 then the A84 to Doune.

I would go further and say that is a lot more scenic, and you see a lot more of the country but wonder what the huge rush is. That route takes you past the Scottish Crannog Centre, which is a highly recommended stop over. And I would even suggest a short divert into Aberfeldy as well.
It is all but 90 minutes from Dalwhinnie to Killin- the A85 junction, then 50 minutes on to Doune Castle, then a further 75 minutes on to Edinburgh- so that is about 3 hours 30 minutes at least without significant stops.

Coming off the A84 just west of Callander you could even add a diversion into the Trossachs proper and down through Aberfoyle then the A873 straight into Stirling. This route could (and should?) be a full day's trip

I'm a bit confused as to your priority here -0 is it sightseeing and visiting Doune Castle and Stirling, as implied in your first paragraph
OR is it enjoying the scenery as implied in the last paragraph....

Stirling can easily fill half as day and Doune castle is going to take 60 minutes plus. I'm also assuming you will need to eat somewhere?

I agree with isn31c and wasleys. Both are scenic, but your timings are way off.

The A9 has average speed cameras on pretty much its entire length. They are always on and I know many people who have received speeding fines (and penalty points on their licence) for exceeding the average speed limits. The limits are 60mph for single carriageway sections and 70mph for dual carriageway sections. Your rental company will catch up with you for the fines and probably add a hefty 'admin' fee.

I think you need to work out which of the various sights on the way interest you the most and plan your route accordingly. But either route will take much longer than you estimate. I drive from Skye to Dunblane at least once a month and know the A9 very well. It's never a super fast drive and nor would I want it to be as there are frequent accidents caused by dangerous driving.

The times I included were from google maps and were for just the drive. I plan on driving past the castles and maybe getting out of the car to take a few pics but not a tour. I’ll be with somebody who has physical limitations so we won’t be getting out of the car much. So… when I say sightsee it really means we are looking for scenic (natural beauty of scotland) and other interesting places/towns that will catch our eye.

In the UK I would never use Google maps to plan a route. Having said that Google maps in the UK agrees pretty much with my timings above. So I don't know if it is configured different!y in the USA, or if the timings you have cited are for the Dalwhinnie to Stirling section of the full journey to Edinburgh. If that is the case then the timings you gave are pretty reasonable as far as Stirling.
But there is some type of disconnect or mis-understanding happening here.
Generally Google maps does not seem to take into account the nature of Scottish roads, or things like speed cameras.
I would always use the AA (same as the American AAA), RAC (their main competitor) or another UK specific route planner.
But anyone who tried for 1:30 to Edinburgh will 100% run foul of the law as skyegirl states- at best. At worst is the very real possibility of causing an RTA.
The average speed cameras are there because the A9 has taken a terrible toll of lost lives. That is why it scares me talking in those terms. I've seen the risks people take.
The driver certainly won't be able to appreciate the scenery aiming for very optimistic timings because their attention will need to be on the road.

Edit - the times were from Dalwhinnie to Doune. Sorry for the confusion. I just checked RAC and the drive time for option 1 is 1 hr 37 min and option 2 is 2hr 12 min. Doesn’t seem that google was that far off.

General advice for visitors to the UK is to add 25% to driving times on Google Maps AND THEN add on time for stops. Driving in Scoltand can be quite slow.

If you aren't actually bothered about visiting Doune or Stirling, then the second option would be my preferred choice. Take it slowly and take the whole day on the trip as there is much to enjoy. If time allows and it is a nice day, you could consider doing a detour along the B846 from Tummel Bridge which will take you along Loch Rannoch and eventually ending at Rannoch Station, one of the most isolated and remote stations in the UK. (Rannoch Moor is the largest area of uninhabited land in the UK.) Check if the Station Tea Room is open (it closes for the winter months) as it gets consistently good reviews on Trip Advisor. Allow a couple of hours for the drive there and back.

Callander ,before you reach Doune, is an nattractive small place and is also is also worth a stop. There are plenty of cafes there too...

I find Google Maps to be good for planning (except for the limited number of destinations in a single route), but I do bump up the driving times. I do all my planning on a speadsheet with 15 minute precision, so for A roads, I just round up to the nearest 15min, for B roads, I bump an extra 15 min, and for single tracks, I bump another 15 min. I generally make stops for wandering around ruins, lunch, etc. as one hour. Things that have a "time needed to visit" (on websites or TA) get marked at that time. In six trips to Scotland and Ireland, I have yet to blow out my schedule due to driving times. A herd of Coo or sheep on the road can use up all my "fat" in one go, so shaving lunch to 45 minutes can easily fix that.