Ariados

Ariados is more of a pest than anything of use in the meta. Very poor stats and lackluster movesets makes this bug a dex filler at best. 

Best PvE Offensive Moveset

• Infestation performs better than Poison Sting in both damage output and energy. 
• Megahorn is the best charge move for Ariados. 
• Lunge is a step down for PvE offense. 
• Cross Poison is nice as a 3-bar move, but has poor damage output. 
• Trailblaze is sub-par even for a Grass Type move, meaning it's pretty bad here.
• Shadow Sneak has no use. 

Best PvE Defensive Moveset

• Infestation has double the base power of Poison Sting, making it better for defense. 
• Cross Poison is good on defense being a 3-bar move, and is the most difficult to dodge. 
• Trailblaze is okay.
• Lunge is easy to dodge, but as a 3-bar move can be used frequently, and hurts Psychic-type attackers. 
• Shadow Sneak as a 3-bar move offers relatively neutral damage on defense, though it's way easier to dodge. 
• Megahorn is generally not recommended for defense due to it being a 1-bar move. 

Poison Sting is more preferable due to its faster energy gains, letting Ariados take advantage of its charge move utilities much sooner. Infestation features above average energy generation, though its damage output is underwhelming, even with STAB.

Added during the GBL Season 8 update, Lunge is a useful addition to Ariados's kit, costing less energy and providing a debuff utility against the opponent. Trailblaze is often the preferred secondary attack to deal heavy damage to Water- and Ground-type Pokemon. Cross Poison is a good low cost move that can occasionally buff Ariados's Attack. Megahorn benefits from STAB and threatens a lot of damage if unshielded, but costs a lot of energy. Shadow Sneak is a pretty bad move.