For connections, and just picking from those: JFK, CLT, MIA
For lounges: JFK (T8 Flagship Lounge), MIA (Flagship Lounge), CLT (??? AC?)
What cabin are you looking to book? That makes a huge difference in terms of aircraft.
For business class, absolutely the 777 and specifically what AA deems the 77W (777-300ER). Best business seat on AA. Second would be the 772 (777-200).
The A330 isn't bad as well.
For the domestic portion, you get what you get. JFK-LAX, as mentioned above, would be the way to go for business or first. Anything outside of that is a typical domestic seat in coach, but better in first. Won't be lie flat outside of the A321T (JFK-LAX/SFO only), but domestic first beats CE by a good margin.