I do think that Feraligatr is still the best choice of the three, but it really only depends on who you like best. They can all solo the entire game with little trouble if you know how to use them so just choose which one you like best.
What I mean by this whole post is that you shouldn't let yourself be swayed by the Meganium haters. She's just as capable of handling the gyms as everyone else is.
Byt I reiterate, use whichever one you like best (even if it is the "girly" looking one) and you should be fine, especially if you want to solo the game.