Meganium is a supporter, Feraligatr is a Physical Tank (ATK/DEF), and Typhlosion is a Special Sweeper.
If you're going to solo the game, Meganium, I think, is out of the picture because it's typing has many weaknesses and it's offensive stats aren't that great.
This leaves Typhlosion and Feraligatr. Now, I like both, but Feraligatr wins me over. Typhlosion is fast and hits hard with special attacks, but it's movepool doesn't help to cover all typings. Nearly all moves learned on level up are Fire and the only good special moves (of another typing besides Fire) learned via TM/HM are Focus Blast, SolarBeam, and HiddenPower (off the top of my head) and they have 70% ACC and 5PP, one turn charge-up, and IV-dependence respectively.
Feraligatr on the other hand, is Physical, giving it access to Crunch, AquaTail, IceFang and SuperPower on level-up + a whole lot of different typed attacks from TM/HM (Earthquake, Dragon/Shadow Claw, IcePunch etc). Finally, to sum it all up it can also learn SwordsDance. So Feraligatr, having 100 DEF can withstand a hit while setting up a SD and then basically sweep. It's typing is also weak to only two types: Grass and Electric which can be taken out with Ice Fang and Earthquake.
SHORT ANSWER/TL;DR = Totodile/Croconaw/Feraligatr owns.
