Heliolisk

Heliolisk is yet another dex-filler Pokemon. Its unique typing does it no favors, and its Attack is just too low to be worth using to any great degree. Best to let Heliolisk bask in peace in your box.

Best PvE Offensive Moveset

• Volt Switch and Thunderbolt is the way to go with Heliolisk, as Parabolic Charge is substantially weaker.
• Mud Slap and Bulldoze... are the same type at least? Still very weak for Heliolisk.
• Quick Attack, Breaking Swipe, and Grass Knot are the bottom picks.

Best PvE Defensive Moveset

• Volt Switch is a great move on defense, and so is Mud Slap. 
• Quick Attack has solid neutral coverage, but not much else.
• Grass Knot has solid counter-coverage, and pairs well with either of Heliolisk's best charge moves.
• Thunderbolt is also great, but needs to pair with Mud Slap most of the time.
• Bulldoze is weaker, but can work well if paired with Volt Switch.
• Breaking Swipe gives Heliolisk a 3-bar Charged Move with great neutral coverage, but its low base power doesn't help it on defense.
• Parabolic Charge is Thunderbolt but substantially worse. It is harder to evade, though.

Volt Switch boasts the best balance overall of moderately high energy generation and decent damage output backed by STAB. Despite its very slow animation, it's the best fast move available. Quick Attack is a step down in every aspect, and can't be Super Effective against anything. Mud Slap is an alternative move that provides useful Ground-type coverage, but lacks STAB damage and has slow energy gains. 

Breaking Swipe is Heliolisk's cheapest Charged Attack and comes with a very nasty guaranteed Attack debuff. Grass Knot is recommended for its valuable coverage against Heliolisk's weakness to Ground-type Pokemon, as well as its slightly lesser energy demands compared to the rest of its Charge Move. However, it can leave Heliolisk with some issues denting certain Steel-type Pokemon. Thunderbolt requires slightly more energy, but is the strongest move available against a neutral opponent thanks to STAB.  Bulldoze isn't a particularly good attack from a stats perspective, with moderately high energy costs, but can fulfill a niche in a scenario where an Electric Pokemon has an advantage in an Electric-type mirror.