I would go with Timid. For the full set, I’d do:
Charizard @ Heavy-Duty Boots / Life Orb
Ability: Blaze
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Air Slash
- Flamethrower
- Scorching Sands
- Solar Beam
For Solar Beam, you can set up the sun with a Drought Pokemon, such as Torkoal or Ninetales. Heavy Duty Boots are in case of Stealth Rocks, but, if you want more power, go with a Life Orb. Timid gives you a much needed speed boost. Air Slash is STAB, Flamethrower is more reliable than Heat Wave in singles, but in doubles I would use Heat Wave. Scorching Sands covers Rock and Electric types, while Solar Beam covers Rock and Water types.
Hope this helps! :)