The last is the best. It's 1.9.5.0 (Official) or 1.9.2.7-6c-pre6 (or pre5) (Oleg's). Oleg's firmware has many more features.
You have to make Factory Defaults after re-flashing with another version (it's strongly recommended, and also each firmware has it's own couple of params saved in CFG (sometimes they meaning is different,so you may have toubles)