Currently on a 3G[S] on 3.1.3 (via Spirit) with baseband 05.12.01.
Trying to upgrade, preferably 4.0.1, and need some experienced advice! What is the current best recommendation to do this?

i know a decent bit about jailbreaking and FWs but controlling a device's baseband is pretty new and confusing to me. it seems like you want to NOT upgrade your baseband if at all possible but is there a point when upgrading or jailbreaking where you have to eventually upgrade the baseband? If not, what are the general rules to "controlling" what your baseband is while still being able to upgrade and JB?

also been having some issues with entire phone crashing and restarting so i am debating on whether to do a clean wipe of the phone and then try to restore directly to 4.0.1 (via SHSH) then JB or if i should somehow upgrade from current 3.1.3 directly through some JB technique? (like Pwnage)