if you just need an emergency phone, go for prepaid. if you call no more than several minutes every week, go for prepaid. if you have the mentality to sneak around for free wifi spots, go for prepaid.
if you just want a peace of mind, use phone to call your beloved one, and check out something on the internet regularly, use google map as your GPS, sign a contract.
there are many prepaid phones, contract and phone companies, just as contract phones. i am using ATT gophone on an unlocked Nokia PDA phone. i used iphone on the same plan before. i am also a long term user of virgin mobile (on Sprint network).