updating firmwire question

[evolancer13#IM]

I got iPhone 3g today jailbroken and unlocked for tmobile, its currently running version 3.0.1 i want to update it, i heard:

4.0 isnt that great
3.1.3 cant be unlocked so cant use my tmobile sim
so 3.1.2 would be better?

should i use pwnage tool or redsn0w?
Also, all the stuff thats already on the iphone will that be deleted after doing this?

-thanks

EDIT
nevermind, i sadly bricked my iphone and just jailbroke 4.0 using redsn0w.