Chikorita, Snivy and Tepig by far. Chikorita's line has already been explained and boils down to a shallow movepool and weaknesses against the first two gyms; interesting concept, but in serious need of a buff, just like Typhlosion and (to a lesser extent) Feraligatr. I love the latter two despite their flaws, but Meganium is just so disappointing compared to them.
And just for clarification before you read on, I'm referring to Overgrow Serperior, not its Contrary counterpart. The latter is amazing thanks to Leaf Storm, but the former just has nothing other than Speed going for it; honestly, Lilligant (with Quiver Dance) and Whimsicott are so much better as Gen V grass types. While Serperior actually has some use thanks to its Hidden Ability, Emboar is absolutely useless aside from its high Attack; all that HP is worthless if it can't even tank thanks to its subpar defences and low Speed. As the third Fire/Fighting type, you'd think Emboar would fill some sort of niche that Blaziken or Infernape can't - simply put, it doesn't.