Flareon

Poor Flareon. It's good on paper, but Fire just wasn’t a great attacking type for raids or gyms. Then Moltres and Entei came along, beating Flareon at just about everything. Flareon is still the next best Fire-type attacker, and it doesn’t require bags of Rare Candy to power up. In addition, with the abundance of Eevee in partly cloudy weather and Fire-type boosts in sunny weather, Flareon has a cost-to-benefit ratio that should not be ignored.

Best PvE Offensive Moveset

• Fire Spin is better than Ember, dealing higher DPS with similar parameters otherwise.

• Overheat is strictly superior to Fire Blast, which in turn trumps Heat Wave.

• Flamethrower has advantages for use in gyms, and Flareon is much less likely to faint with wasted energy if running this move.

• Last Resort has little to no offensive viability.

• Superpower is meant for PvP. 

Best PvE Defensive Moveset

• Fire Spin is basically just a better version of Ember.

• Superpower is preferable for defense due to its coverage against Rock-type attackers, but is limited to Elite TMs and Community Day events. 

• Flamethrower and Last Resort are alternative options for defense. The former has an earlier damage window, making it more likely to hit inattentive attackers.

• Of Flareon’s 1-bar charge moves, Heat Wave is weak but the most likely to hit the attacker.

• Overheat and Fire Blast are very easy to dodge and don’t work well with Flareon’s frailty.

Fire Spin is a great move in PVP thanks to having great overall performance which allows it to deal solid damage and charge Flareon's moves reasonably fast. Ember trades a little bit of energy generation in favor of slightly more damage output. 

Flamethrower is Flareon's balanced general-purpose charged move. Overheat is much stronger for the same energy cost, but its self-debuff makes it more difficult to use. Superpower is a great coverage move for Flareon, allowing it fight back against Rock-type opponents, though it also has a self-debuff issue. Last Resort demands more energy and risks Flareon being completely resisted by Rock Pokemon. Heat Wave and Fire Blast are poor choices for PvP.