[Kamen Rider Lucha]

Hmm... I don't feel fully qualified to judge, having only seen 8 of the 18 series with 6th rangers. From the shows I've watched form beginning to end (Dai, Oh, Magi, Shinken-through-Ninnin), ToQ6 is probably my favorite 6th.

Although, if one were to consider Car's VRV Master a 6th Ranger (I don't know that anyone does), he'd leap straight to the top.

Looking over this list, I find myself realizing that 6th Rangers are rarely my favorite (even though they're pretty much all the best looking heroes of their seasons).