With the game now in Generation 6 that means we can now technically have full teams of just Starter Pok'emon... except with the introduction of Mega Evolutions the Starters are no longer equal.
I'm not going to be talking about special Starters like Ash's Pikachu or Gary's Eevee. Just the main three starters for each generation.
Now lets assume here for a minute that you have a full team of Grass Starters.
Venusaur: One of the first Pok'emon to get a Mega evolution.
Meganium: No Mega evolution... which would be funny if it did considering it already has Mega in it's name.
Sceptile: Originally didn't have a Mega but was introduced with OR and OS.
Torterra: No mega evolution
Serperior: No mega
Chesnaught: No mega
A full team of Fire Type Starters...
Charizard: Not one but TWO Mega evolutions to choose from. You'd have to trade between X and Y to get both Mega evolution stones but it is possible to change between them as needed.
Typhlosion: No mega
Blaziken: The only gen 3 starter to get a mega in X and Y. You need OR or OS to get the other two.
Infernape: No mega
Emboar: No mega
Delphox: No mega
And now the Water starters...
Blastoise: One of the first to get a Mega.
Feraligatr: No mega
Swampert: Only in OR/OS.
Empoleon: No Mega
Samurott: No Mega
Greninja: No Mega
Now Grass and Water are pretty much even. At least in terms of the over all team. They have the same number of Pok'emon who can Mega Evolve and the same number of Mega Evolutions possible.
Fire on the other hand has this unfair advantage from day one to now. It's a little more evened out now with the addition of the other two Gen 3 Starters which couldn't Mega evolve before but you still have two options for Charizard. He's one of only two Pok'emon (3 if you count the Male and Female versions of a Pok'emon from the same evolutionary line.) who can do that.
The three starters have up till now always been pretty much equals. They all had three stages of evolution and no matter which one you choose your rival is always going to take the one you're weak to. So the only real deciding factors in choosing your starters was personal preference. For me, back when I use to play this game, I always had a personal preference for the water types being that I'm a Pisces. Though I've always liked Charizards design as well, it always bothered me that he wasn't a Dragon type... though now with Mega Charizard X he is. I've never been a big fan of the Grass types... except in Gen 5 which I never actually played but Serperior actually has the best design there in my opinion. The only time I would ever actually pick grass over the other two.
Anyway, with the Mega Evolutions it's no longer even. Of course you're going to want to pick the Fire Type team because they're the strongest. Again not as much now but you still got two options with Charizard where you only have one choice with the other two. If you've always wanted him to be Dragon type like me you can go Mega X. Except if you have a type match up Dragon is weak to then you can go Mega Y.
And why would you ever even use the Starters who can't Mega Evolve? I mean you can choose not to Mega Evolve any of them just to keep things even but then what are you going to do when you have to fight a Mega Evolution. Or someone with a whole Team of Mega Evolutions? Your Starter team is going to die.
Ni, peng, nee-wom! Ecky, ecky, ecky, pakang, zoom-ping! Baa weep grahna weep ninny bong!