I am currently on iPhone 4, 4.0.1, BB 01.59.00, JB thru Jailbreakme.com, running windows XP. Everything works great. are there any compelling reasons to upgrade, re-JB, and go thru the hassle of re-installing and tweaking all my apps? if so, what is the definitive best way to do this.
That depends if any of the new features appeal to you. 4.1 added gamecenter, 4.2.1 added airplay and airprint and 4.3 added personal hotspot. If none of those appeal to you then it doesnt make sense to update yet.
4.1 is way better than 4.01, it fixes Bluetooth problems and I think dropped calls a little. I don't know how much better 4.3.1 is than 4.1 but if I were you then i would upgrade. You can upgrade and preserve your baseband if you need an unlock too.