It depends on your requirements and style. I'm still on the xpro mk1. I believe mk2 offers minor subtle improvements and is an obvious upgrade but right now I have no need. What I really like about it is the light touch on-off switch (super important to me - no movement on tripod), and physical buttons for all 5 groups. I usually fit within 3 but used more on occasion. It just works well. They weight nothing.
X3 is defnitely on the small size. Screen is nicer but really could be bigger. I will wait for x3pro. Youtube is full of hands on demo videos if you would like a deep dive into functionality. Personally I found it all too fiddly and didn't like on off functionality at all.