Ninetales

Ninetales lacks adequate stats for the PvE meta, especially since various Fire-type Pokemon have been added to the game with superior stats. It's not particularly amazing for gym defense either, which is rather unfortunate. 

Best PvE Offensive Moveset

• Fire Spin is superior to Ember or Feint Attack, offering the highest DPS for slightly less energy gains. 
• Weather Ball Fire is the best charge move available, and also the most consistent as a 3-bar move. 
• Overheat is a step down, but still serviceable if TMs are lacking. 
• Flamethrower, Heat Wave, and Fire Blast are inferior to Overheat, though Flamethrower can be more consistent than the rest due to requiring only half as much energy.
• Psyshock, Scorching Sands, and Solar Beam don't get STAB and should be TM'd. 

Best PvE Defensive Moveset

• Fire Spin is the best fast move on defense, featuring the highest base power. 
• Feint Attack isn't particularly impressive, but at least it's less likely to be resisted by attackers. 
• Weather Ball Fire would be best charge move for defense thanks to it being a 3-bar move, but the fact that it shares a type with Fire Spin makes it easy to wall Ninetails out.
• Scorching Sands is the overall best option on defense
• Flamethrower and Psyshock are more likely to be used before Ninetales faints, the former benefiting from STAB while the latter offering greater coverage. 
• Heat Wave, Fire Blast, Solar Beam, and Overheat are too slow to be effective on defense. 

Fire Spin offers slightly superior energy generation, while Ember sports slightly stronger damage output. Either can be viable, though the latter requires an Elite TM. 

The addition of Weather Ball (Fire) is incredibly important for Ninetales, as it offers a cheap energy charge move option, and can be used frequently. Scorching Sands offers good coverage alongside a relatively low energy cost, making it an optimal pick. Psyshock costs a moderate amount of energy and provides alternative coverage. Overheat is powerful for its moderate energy cost, but doesn't provide extra coverage, and can be difficult to use due to its self-debuff. Flamethrower is a downgrade in performance compared to Weather Ball, while Fire Blast, Heat Wave, and Solar Beam demand way too much energy to use (though the latter can surprise Pokemon that Ninetales is weak to).