I have mixed feelings about United's A319 aircraft. Seats 21A and 21F do not have a seat in front of them, so you have about 50 in of leg room. The first class cabin however has only 8 seats. It's always a difficult flight to clear an upgrade, especially when flying hub to hub or at peak times. On my most recent flight, my upgrade cleared at the gate (1K on a Q fare flying on a Sunday morning DEN-SFO if you are interested).
United A319 Seat 1A
The first class seat in United's Airbus fleet is very comfortable and has plenty of recline. There isn't too much legroom, but the bulkhead for 1A and 1B has a cutout for a little more space. No meal was served (United A319 lunch review) and I was able to get in almost two hours of work on the flight. The flight went fast and was a nice trip all around with some fun views coming into SFO.