What is the best moveset for delta charizard?
It depends. If you are going to Mega Delta Charizard then I find the best moveset to be:
-Draco Meteor -Lunar Cannon -Sludge Bomb -Frost Breath/Flamethrower
If you are not using the megastone then I recommend:
-Draco Meteor -Shadow Ball -Sludge Bomb -Frost Breath/Flamethrower
Which move would you suggest flamethrower or frost breath?
Depends on your team. Pick the one you need more coverage for based on the moves of the rest of your team.