His last three films have moments of Fight Club-esque craziness but they're way better films than that one. I guess it's kind of a maturing process. I hope B never matures. He seems like a kind of manic 16 year old that has mad skills and energy. A, I have no idea what he would be like if going by his films. They're pretty disparate as far as subject matter and technique goes. His films have gotten steadily better, though, so that's something.
I think the technique in As films isn't all that disparate - at least in terms of the end. He always tries to invest the audience in the immediacy of the onscreen action. To borrow from Strange Days - You're there, you're doing it, you're feeling it. Via the camera and editing he creates a more active, viceral experience as opposed to a passive viewing one. I don't think the other two use their inherent frenetecism to this end nearly as much.
B loves the urban rhythms and taking different genres for a spin. He's also very community focused. Almost always the individual rejoins society at the end of a Boyle film. Ewan
chooses life, DiCaprio
connects with his family via email, Murphy
gets rescued & sacrafices for the benefit of mankind, Franco
escapes from isolation. Society is the safety that each person must return to, the collective wins.
Fincher likes Serial Killers!