I picked froakie as my starter, and yea protean greninja is a fast, versatile attacker, not once has he swept/dominated in any major fights, so to me he seems strong, but balanced. also his level up movepool isn't that great, so it takes a fairly long time for him to actually get good. frogadier especially felt quite weak while I had him. Gyarados especially is a lot stronger. Moxie is an incredibly powerful ability and gyarados also has great speed boosting with d-dance. krookadile and honchkrow are more limited because of their lack of speed boosting, but my friend has been sweeping many tough fights with sticky web galvantula + moxie honchkrow. gengar just has excellent special attack and speed with a good movepool and decent defensive typing, but should probably be included back into the game around where we currently are. greninja is a bit faster than gengar but has noticeably less power behind his attacks.