They all have their ups and downs. Your best bet is to read up on each model and decide for yourself. There is no "best". Everyone has their own likes and dislikes.
i agree with the above posts. there really is no "best" (err blask?) blackberry. every person's needs and tastes are different. some people like larger phones, some people (like me at a staggering five-foot-nothing) like smaller phones. also some people prefer suretype to the full qwerty keyboard found on a lot of berries. it all just depends, ya know.