Serperior

Serperior is the Grass-type starter of Gen 5, but isn't too exciting due to its poor stats. An ATK stat lower than that of Meganium's is a pretty clear indication that there might not much use for the serpentine Pokemon.

Best PvE Offensive Moveset

• Vine Whip takes advantage of STAB and is the optimal fast move for Serperior. 
• Iron Tail trails behind in performance and isn't as useful partly due to lacking STAB.
• Frenzy Plant is objectively great, and the charge move of choice.
• Grass Knot is Serperior's best non-elite charge move and hits hard with STAB.
• Leaf Tornado does get STAB, but has very bad damage output. 
• Aerial Ace is a lackluster move. 

Best PvE Defensive Moveset

• Iron Tail hits quite hard on defense and is more optimal than Vine Whip.
• Frenzy Plant hits for maximum power.
• Grass Knot is weaker, but still usable.
• Aerial Ace and Leaf Tornado perform roughly the same on defense, and are okay as 3-bar moves but don't deal as much damage. 

Vine Whip is the superior pick due to significantly better energy gains along with STAB.

Frenzy Plant is Serperior's strongest move in a vacuum, as well as in practice. Aerial Ace provides good coverage against other Grass and common Fighting-types, but is generally a weak move. Leaf Tornado is a bad move from a damage perspective, but if you're willing to forgo Aerial Ace's coverage, it can be worth throwing out to fish for debuffs. Grass Knot can technically be run, but it's a significant downgrade over Frenzy Plant.