Metagross

Metagross is the Dragonite/Tyranitar of the third generation, boasting high stats across the board. With a weak movepool, it took some time for this generation's pseudo legendary to shine. But thanks to the October 2018 Community Day, Metagross finally became the powerhouse it's stats wanted it to be. Meteor Mash, a near-clone of Venusaur's Frenzy Plant, is an insanely strong charge move that absolutely crushes everything that's weak to Steel. These factors together make Metagross an absolute staple raider. On top of this, Metagross can also run a Psychic Type moveset very effectively, giving it a lot of utility for players with a second charged move unlocked.

Max Battles

Thanks to its excellent overall stats, Metagross is a wonderful all-rounder choice in Max Battles. Whether you want to fire off a Max Attack or defend/support your team with Max Guard, Metagross can flexibly adapt to either role much better than most Pokemon in the early metagame. Metagross is also a contender to remain useful in the Dynamax meta, as well. While it does have to worry about Gigantamax formes of Melmetal and Copperajah in the future (Duraludon and Corviknight don't have Steel Type G-Max moves), it will likely always retain utility as a Steel Type Dynamax for the foreseeable future, and as of right now it's also a good Max Mindstorm user as well.

Metagross's one downside is its lack of Fast Attacks with a 0.5s duration, so it isn't amazing at charging up the Max Meter. When Metagross is defending its team with Max Guard, its teammates should try to make use of glass cannons that can charge up the Max Meter quickly.

Best PvE Offensive Moveset

• Meteor Mash is a top tier move with similar stats to Frenzy Plant (the best Grass-type charge move), and it should be paired with Bullet Punch for maximum Steel Type DPS.
• Psychic makes Metagross a worthwhile Psychic Type attacker, and should be paired with Zen Headbutt.
• Flash Cannon is a sub-optimal move.
• Earthquake lacks STAB and type synergy.

Best PvE Defensive Moveset

• Zen Headbutt has the higher power and is better than Bullet Punch on defense as a result.
• Meteor Mash is powerful enough that it bests all of Metagross's other charge moves. 
• Psychic is a good, 2-bar move that deals super effective damage to Machamp, making it a fine choice.
• Flash Cannon is off type with Zen Headbutt and doesn’t leave Metagross toothless against Dark-types. However, it is very sow and not very powerful.
• Earthquake has the same power and arguably more useful typing, but is super easy to dodge.

Bullet Punch has solid damage and above average energy gain. Avoid Zen Headbutt at all costs.

Meteor Mash is an incredibly powerful, if somewhat expensive move, and is core on any Metagross set. Sadly, if you’re missing Meteor Mash, maybe leave this metal menace out of your matches. Because Flash Cannon isn't very good, we round out this set with Earthquake which gives Metagross the tools to deal with fellow Steel-types and any potential Fire-type counters. 

With the September 2019 update to Psychic (90 Power/55 Energy), Metagross at last has a second set worth consideration. While it may not provide the valuable coverage of Earthquake, Psychic is cheaper and provides a second powerful STAB move for neutral damage against some Pokemon that resist Meteor Mash.