Pros and Cons: Blackberry, Samsung Blackjack , iPhone and Others?

So, I wanna buy one of these but I don't know which one's better. I want something that can e-mail and surf the net and maybe play some music. I want a good phone as well. Which one has faired best from y'alls experience? Please give me both pros and cons! Which has best battery life? I don't really care a whole bunch about the look. I want whichever one functions the best. Also, I want to buy 4 of them, so please give me any heads up you may have on good deals! Also, would it be alright to but these from online? If so, which website would y'all recommend? Amazon, Ebay...??? Thanks for any advice at all!!! I have At&T