Flareon 100% - FS/FT or FS/OH

On Arcanine you have a case but Flareon is much better in everyday use with OH. A %100 Flareon deserves OH.

Edit: Arcanine with dark moves may prove better, but today it's sub-par to tiny Flareon.

Just don't get Fire Blast and you are OK.

Flamethrower is less risky, but Overheat deals more DPS.

If TMs are adding up, use one. If not, ft is great. I have a maxed ft Flareon and a level 30 oh Flareon. Use them both.

If you need raw DPS, Overheat is better.
But Flamethrower has several advantages.
1: Multi bar, can be used with 50 energy, no over-charging energy bar
2: Short duration, can even fit in between Exeggutor's Confusions
3: If Flareon has 60 energy and is about to faint, you can still throw a flamethrower, but not an overheat.

I have a F/O that I previously powered up for Blissey and a F/Ft that I recently powered up for Articuno. For regular gym fighting, F/O is great against Blissey with Z/Dg, but against most other defenders that I want a fire attacker for (especially after a little motivation loss) I prefer F/Ft for faster energy use, less wasted energy, and less overkill.