Lucario

Counter + Shadow Ball and one of Power-Up Punch/Thunder Punch/Close Combat/Blaze Kick

Counter and Bullet Punch are both good moves stat-wise, but the former offers more relevant coverage and also sports better damage output. 

Power-Up Punch can be used to bait shields and apply an ATK buff, but its poor damage means it rarely punishes opponents for not shielding. Close Combat has been more popular due to its significant damage potential, despite its significant self-debuff. It is recommended to charge enough energy to use two Close Combats in a row, rather than using it immediately when available. Shadow Ball is preferred for its mostly neutral coverage, but it's also valuable against most Pokemon that would resist Fighting-type damage. Blaze Kick hits a number of types for Super Effective damage and has a low energy cost, making it a worthwhile option. However, Fire has some coverage overlap with Fighting, making it a bit less valuable than it appears on the surface. Thunder Punch can hit some Flying- and Water-type Pokemon for super effective damage.

Shadow Ball itself isn't necessarily mandatory if the metagame lacks good Ghost- and Psychic-type targets. Lucario can utilize two of its other Charged Attacks to better suit itself in said metagame.

What about Aura Sphere? 

Added with the Dec 11, 2019 move rebalance, Aura Sphere features identical stats as Shadow Ball, but instead is a Fighting-type move which has STAB. While this may seem quite powerful (and it is), the increased energy cost compared to Close Combat makes it more difficult to access. It is however quite good for Rocket battles if Lucario lives long enough to use it.