Adv is by far Dugtrios best gen. It faces absolutely no competition in its role as a revenge killer and a whole lot of OU is at risk from it- it actually has half of the tier under its dominion. It's more than often a teams only answer to threats such as Heracross and Raikou since these pokemon are notoriously difficult to stop without dedicated walls. Additionally, with a complete lack of Scarf or priority in Adv, Duggy can quite happily give itself the power it so loves from Choice Band to aid its revenging capabilities, and with the lack of the physical/special split it can run Hidden Power to deal with whatever it feels- by far the most common option is Bug, since it still deals ~70% to the most defensive of Celebi, making it another victim to Dugtrios selective wrath. Dugtrio also checks monoattacking Zapdos, a very common sight in Adv, though Dugtrio is vulnerable to the spikes that Zapdos will always be paired with.
Not only that, but it forms a part of the well known Aero+Duggy and Magtrio combos, both of which fill different niches within teams- whilst Aero+Duggy works on being a one time answer to removing a threat of your choice, Magtrio is an incredibly potent duo of threat removers, which between them are capable of removing pretty much any wall with the game (depending on Magnetons set).
Dugtrios main weak points are, of course, Choice Band locking it into moves, forcing it to switch out once it kills something, and the fact that it can't take any hits other than Rock Slide, Neutral unSTAB special attacks, and Blissey Ice Beam-even then, all of them leave Dugtrio severely wounded and consequently compound his ability to come in on Spikes again, another weakness. However, rarely should Dugtrio have to worry about these problems as he should only be coming it to hit and run.
Dugtrios presence and utility within Adv is very strong- almost dominating- and many a time people have built teams that would otherwise be great, but have a huge weakness to one thing and one thing alone- Dugtrio. By far the best crutch for a Dugtrio weak team is Porygon2- with its very good bulk and Trace, P2 can easily come in and revenge the revenge killer with Ice Beam in an ironic twist, whilst also filling a role in the team by checking threats like Salamence, Gyarados, Flygon, and Vaporeon, whilst being an all round pest. Alternatively, one can build their team in a way so that it is only weak to the weaker of Dugtrios moves (using Heracross and Celebi) and then making use of Sharpen Porygon2, who can set up on Hidden Power Bug/Aerial Ace all day, not even being 2HKOed by consecutive crits, and then becoming a downright menace, ravaging teams with +6 STAB Returns and great bulk that is near impossible to OHKO. Essentially, if you need a way to stop Dugtrio from dismantling your team bit by bit, look no further- Porygon2 is the one and only way to reliably stop him dead,, limiting the damage it does to your team, and is one of the main reasons its usage has shot up in recent times.
So yeah. Adv Dug. Went off for a bit on P2 because it is about the closest thing to a counter this thing has and really deserves more recognition for it.