ROFLcopter
I don't know why people are saying Charizard is tier 1. The best build is like tier 2.5. Anything Charizard can do other decks can do better. Charizard is a beefy beatstick at best. It has no finesse, no disruption, gets walled by stuff like Spiritomb and, next format, Vileplume, is difficult to setup, has energy problems considering its primary engine, Ninetales, requires a discard, forcing you to run more energy, which you then draw into in your opening hand. People still run it with Ninetales, right?
Despite what people seem to believe, it has few good matchups. It's good against Jumpluff if it gets setup properly, which is a large "if." It gets destroyed by Sablelock, since Sablelock makes it even more difficult to setup what was difficult to setup to begin with. LuxChomp is tough, since they can take out your support (Ninetales) early and proceed to switch around and Poké Turn up guys you have trouble OHKOing. Gyarados obviously crushes you. Donphan can go either way, but it's so much easier to setup that I like it better in this matchup.
Straight Champ is not a difficult matchup, considering they can't hit you especially hard, but that's on the expectation that Charizard gets setup. See, my biggest problem with the deck isn't that Charizard is a bad attacker, but that it can't abuse DCE, and dropping stuff like Uxie hurts you. It's also very susceptible to bad starts which, being generally unlucky, I don't like at all.