0448 Lucario

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. However its poor damage output makes it less appealing to use. 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.

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. 

Lucario is a Fighting/Steel type with poor bulk but plenty of resistances. A major weakness against other Fighting-types often makes Lucario a risky pick to use due to the likelihood of it losing, but its powerful moveset, good shield pressure, and valuable coverage makes it very appealing to use wherever it's eligible. The nerf to Power-Up Punch has hurt Lucario's overall performance, but not significantly enough to knock Lucario out of relevancy. The update to Close Combat enables Lucario to possibly threaten KOs with its high offensive stat and STAB, though its low survivability prevents it from staying on the field too long. 

As a Fighting-type, Lucario's access to Shadow Ball is incredibly valuable in a meta that's dominated by Ghosts, Darks, and Steel-types. Being able to threaten Giratina while also serving as a strong escort for the king of Ultra League makes Lucario irreplaceable by any other Pokemon. Due to its Steel-typing however, Lucario will often lose to just about every other Fighting-type, which can make it riskier to use. The lack of sufficient bulk is also a major concern for Lucario. Since the Power-Up Punch nerf, it's lost a large amount of power, relegating it to being a more niche pick, but still usable.

Lucario's low max CP cripples it in Master League. While its dual Steel/Fighting typing and fantastic moves should make it strong, it just dies to far too much. Sadly, there are so many better options.