Emboar's Flamethrower ends up doing a bit more due to the extra power it offers. In conclusion, Flamethrower will do more. But I highly recommend that you use Fire Punch over Flamethrower, as Emboar's attack will increase quite fast due to its high base attack.

Is heat crash better than flame charge for Emboar?

In-game, Heat Crash does just fine. My Emboar had Heat Crash and he obliterated. But, if you want a move with a consistently higher base power, then Flare Blitz is technically the strongest move Emboar can learn.

Is flame charge good for Emboar?

The only Fire-type fast move that Emboar can learn is Ember, and the best charged move is Flame Charge. Emboar can also learn Heat Wave for its charged move, but Flame Charge is far more efficient for fights as it charges much faster.