I've tested many many ROMs (stock, CM7.2, CM9, ...) and here is what I can say :
Battery / Stability wise, I would say "Adrenaline" is maybe the best.
No bug at all, rock stable, extremely smooth, and partial ICS look available.
I have been using it for several weeks, and I'm not planing to switch until an ICS ROM becomes available for Gio that is stable and battery friendly.
Phiezx CM7.2 is also really great.
It is not as smooth as Adrenaline, but offers more tweaks.
I've tested CM7.2 + Adrenaline Boost but it is still not as smooth as original Adrenaline.
GalaxyICS's CM9 is very promising, extremely smooth, looks great, but obviously it is not suitable for daily use (battery life is miserable, many bugs and stability issues).
I've not tested Particle, Jonas, and all other ROM that are not maintained any more.