Newest release (OEM, not cooked/custom). I didn't want to mess with custom/cooked ROM's because I was too afraid of not knowing what to do if I ever bricked it by mistake (while making adjustments). I also use Sprint NAV a lot and some of the ROM's disabled that.
I did custom tweaks for looks and TouchFlo3D formatting, but that's about it. If I hadn't gotten so frustrated with the phone at one point, I probably would've tried Android. I'll still probably try Android, prior to getting rid of the phone, just to get used to it for a week or so, but we'll see. I don't have as much time as I used to for customizations, which is why I'm sold on Android and the EVO.