Jailbreaking is always a picce of cake, dont forget the old JailbreakMe 2.0 :)
and i my experience its very very hard to brick an iphone to a non recoverable state.
I agree
although iphone 3gs is a 2 year old phone its the better option among the three, but i say you should wait for Galaxy S II to lunch and it should cost around 28k i hope ;)