I’m almost 100% split between the two. I would say that React Navigation has (at this second) a more stable API because of a recent rewrite & has a lot of good maintainers & contributors, you can do whatever you want with it pretty much.

React Native Navigation V2 is still very new as far as it being a rewrite of a previous version so I would assume that not everything is yet fleshed out. The good thing is that the team working on it is amazing & are going to get it to where it needs to be soon. Also, React Native Navigation is a native solution whereas React Navigation is JS based.

Bottom line is you really can’t go wrong with either one imo.