Given the current situation, what currently available Bitcoin clients are the most likely to follow the longest chain one month from now? I am completely lost with the various BIPs and what exactly every client implements. So given the current situation as of July 2017, what currently available Bitcoin clients are the most likely to follow the longest chain by end of August?
We don't know what will happen, therefore it is hard to say which client will be on "the longest chain".    


Core is scool with bip141, so it will follow that.
Segwit2x hard fork will be using BTC1.   
USAF could hard fork as well so that client will be for that chain. 
BItmain's BitcoinABC will have their own client (I'm not sure what that client will be/is called).