yes, LAx has the best connection also (CX has 2 flights/day in the past, now reduced to ~1.5 i think)

also make sure your are on the 3-class flights (but i think AA11 is gone now? what a pity)

JFK transit is good because you spend more time on CX. but the transit at JFK is no fun at all
1. BOS-JFK often delay in the afternoon/evening
2. BOS gates for AA EAGLE is away from the lounges (with the new security line it means u can't practically wait at the lounge in BOS)
3. the little Embradier (Y class) is not fun, and it spends 20 minutes on the ground at JFK after landing (total flight time in air < 60 min)
4. connection at JFK is terrible, different terminals (T7 for CX vs T9 for AA). if u really going there, make sure you go for the oneworld shuttle downstair at gate41/JFK, which will transport you to CX/BA gates (and by-pass security)