Leafeon

Leafeon would be a more impactful Pokemon if there didn't already exist Community Day starters and a legion of other great Grass Pokemon. If you have those, then there's no reason to use Leafeon. In contrast to some other Eeveelutions, Leafeon is less accessible than its competitors, which negates one of the benefits of being an Eeveelution. It's not a bad Pokemon, though.

Best PvE Offensive Moveset

• Razor Leaf is Leafeon's best fast move.
• Bullet Seed is a step down in overall offensive performance. 
• Don't use Quick Attack.
• Leaf Blade is the superior charged move in almost every respect.
• Solar Beam and Energy Ball are serviceable, just not optimal.
• Last Resort isn't meant for offense. 

Best PvE Defensive Moveset

• STAB Razor Leaf is just so much stronger than Bullet Seed or Quick Attack.
• Leaf Blade is used often, hits fast, and is fairly strong.
• Energy Ball and Solar Beam are easier to dodge and cost more energy.
• Last Resort is quite easy to dodge, and doesn't offer very valuable coverage. 

Razor Leaf and Bullet Seed are almost polar opposites of each other. The former features very high raw damage with STAB, while the latter offers neutral below-average damage for much higher energy gains. Quick Attack lacks STAB and can't be Super Effective against anything. 

Leaf Blade is Leafeon's best charge move, as it gets STAB, costs low amounts of energy, and has a high DPE. It's also superior to all of Leafeon's other Grass-type charge moves. Last Resort is recommended as the second choice due to it providing neutral coverage.