Overheat goes on Fire Types that attack physically more, or on non-Fire types that want to OHKO things weak to Fire (Primeape, for example, uses Overheat to whipe out Skarmory =0)
Fire Blast>Flamethrower on Fire Types that are basically hit and run. Having 85% accuracy, it is higher than Hydro Pump, Thunder, and Blizzard, therefore making it the better of the 120 power attacks (Solar Beam has 100% but it takes two turns, so meh). It also has 10% chance to Burn, so thats always a nice bonus. Fire Blast goes on monsters with high Special Attack and can die easily.
Flamethrower goes on Fire Types that don't have massive Special Attack, but can last battles longer.
Heat Wave (on the monsters that can use it) is my favorite move, because it has good accuracy like Flamethrower, has 5 more base power, and has 20% chance to Burn, which is higher than all other Fire moves, other than Sacred Fire (50% wtf).
So, basically, DrumZard should get Blast or Overheat. Flareon should get Overheat. Entei should get Flamethrower. Houndoom should get Blast. Special Attack Charizard should get Heat Wave. Reversal Blaziken should get Heat Wave. Typhlosion should get Fire Blast. There are others, but yeah.