Of BA's A3xx series aircraft the A320 has the least extra legroom at the exit rows. I would concur with c-w-s that row 11 would be the best, as row 10 can't recline into you, but you still can recline if you wish. I would, however, make sure that you are early on board the aircraft as you will need to put everything in the overhead locker for take-off and landing. Locker space is always at a premium on board, and if you don't get your stuff in the overhead then you run the risk of it going in the hold.

The A319 has the best combination of standard seat config with good legroom. Whilst the A321 has the most legroom at the doors, including two seats at row 22 due to missing seats in row 21, the seats are narrower due to the tray table being in the arm rest and I just don't find them as comfortable.