I would like to do it on 4.2.1 but know that they can run a little slow on it as the processor can't handle it very well, and that you have to update the baseband to 6.15 which there is no turning back from.
Any advice as to which iOS I should jailbreak it on or information on just how slow running iOS 4.2.1 on a 3G is would be appreciated.
Thanks