Should i get the I-phone 3G?>-<?

I have till May of 2009 or sooner.i am with sprint right now and they suck.Heck i cant even get any service in their own store.that's kinda sucky.but i am going with AT&T because our house phone is with them.and i want a phone with fast stuff and slim that looks cool.my sister has the old one and its really cool.she doesn't like it tho but what does she know.so if you could give me some ideas of what kind of phone to get with AT&T.Please tell why i should get the phone and what phone to get.P.S i am 13.