3.02 is the flagship version, about the only issue with it are the helos occasionally crashing.
The 4.xx playtest is a very advanced version with a lot of new features. It doens't come with documentation, but you can find instructions of most of the controls here on the forum. In my observation, the homing functions Mk50s and Mk54s are a bit buggy. I think this version is fun to play with as it may well be the shape of things to come (a blessing, not a curse
), but for competitive purposes I'd stick with 3.02 for now.