I use v4 a lot, but it really isn't ready for prime time. It is getting closer, but every bot I have worked on I have run into multiple bugs. Anything serious, I'd stick with v3, I hate to recommend that as the code isn't cross compatible and I'd rather put effort into learning and using the new v4 environment but I just wouldn't use v4 for something you really need to be stable and frustration free. That being said, v4 is a HUGE improvement from v3, once it is stable it should be a big improvement over v3.