Aggron

Aggron is basically a walking meme in Pokemon Go: it's not as hated as Blissey, but pulling one out in a raid is likely to garner a few funny looks from many players. Its resistances and high defense combined with a solid moveset can make it a viable anchor in some raids, but note that it is definitely below other counters in terms of DPS. Even with addition of the incredible Meteor Beam to its movepool, it still lags behind many competitors.

Having one good Aggron raised may not be horrible, as Mega Aggron can spread its mega boosts for a very long time, but it's still not a good DPS option and competes with monsters like Mega Lucario.

Best PvE Offensive Moveset

• Meteor Beam pairs well with Smack Down if Aggron is ever needed for Rock-type coverage. 
• Heavy Slam shares typing with Iron Tail to fulfill a niche Steel-type role.
• Stone Edge is worse than Meteor Beam.
• Rock Tomb is a downgrade. 
• Dragon Tail doesn't get STAB, and consequently performs worse. 
• Don’t use Thunder on offensive Aggron.

Best PvE Defensive Moveset

• Iron Tail usually beats Dragon Tail on defense due to STAB, but they are close.
• Smack Down gets STAB and offers more coverage, but is resisted by Machamp. 
• Rock Tomb is quite slow and lacks damage, making it poor for defense despite being a 2-bar move. 
• Heavy Slam is a 2-bar Charge Move and can be tricky to dodge.
• Stone Edge is very hard to react to, but a demotivated Aggron will struggle to use it against its counters.
• Thunder is like Stone Edge except with no STAB and a different effectiveness profile.

Smack Down is preferred for its high damage output backed by STAB, in addition to good coverage against common typings. Dragon Tail generally performs worse partly due to lack of STAB, though there may be niche cases where you'd want the Dragon-type damage and extra energy generation.

Meteor Beam is an incredible move - its superior DPE and guaranteed Attack boost is worth the slight cost increase over Stone Edge. Heavy Slam is Aggron's cheapest Charged Attack, although it doesn't provide much coverage and isn't exactly cheap or strong. Thunder is Aggron's strongest option against Steel- and Water-type targets, but a super effective Thunder is only 11% stronger than a neutral Meteor Beam. The addition of Rock Tomb following the GBL Season 10 update is unimpressive, as its poor damage output and high energy cost discourages its use despite its new debuff utility.