I think i like assasins creed 2 more, especially because you can ride on horses in the city, because of the "wolves" and because it has a lot of things you can do. I haven't finished the game yet but it was sweet from ezio how he saved a 'courtisane'.
Well the multiplayer for Brotherhood basically wins it all. And plus the Armor of Brutus is awesome. But AC2 had a better story but I'm going to have to go with Brotherhood. It sucks though how Ezio loses Altair's armor in Brotherhood.
I think AC2 was better: there was more places to go to (forlÃ, florence, etc.) after you'd discovered them (whereas in AC:B you could only go to other places during faction missions), it was slightly longer than brotherhood as well and the introduction really showed what Abstergo was like outside the animus room.