I used greninja in my current playthrough and I was quite happy with it throughout. Early on, changing your type is extremely useful, even if your moveset is like water pulse, smack down, lick and quick attack(the latter two can be quite fun to invalidate normal/fighting/ghost attacks, even if they're weak). In the midgame it suffers a lot from the lack of good TM's, but sometime around the agate circus it becomes good again thanks to surf, grass knot and dark pulse (among many other options).
On the other hand, blaziken is imo downright broken. Ever since it got Speed Boost, it has been in Uber, and for good reason.
