The one factor that could hurt you with AA's program is their free comped domestic upgrades for top tier flyers. For instance, today I got the last upgrade seat on DFW-SFO with 22 people on the upgrade list. If you're looking at upgrades or extra legroom, with a lower status, you might need to accept that you'll need to try and prebook emergency exit rows, as AA doesn't have a zone with extra legroom like UA does, and not expect a lot of upgrades.

Unlike UA, though, AA doesn't have any nonstops to the DC area (UA has SFO-IAD), so you'd need to connect somewhere to get there. I flew via ORD to get there and came back via DFW.

I'd suggest you look at some other items besides comfort.

1. Lifetime status---AA counts every miles you accrue, not just flight miles
2. Award travel---AA has off peak Europe and South America awards for 40K, and One World awards, which are different than partner awards, can be very versatile
3. Lounge access--all the airports you list have Admirals Clubs, with DCA having some of the best staff in the AA network
4. Routes--you'll find AA weak into IAD, where UA is the major player there---AA has a lot of flights into DCA, though---also look at what type of aircraft you would fly with either carrier (mainline vs regional jets)