Ooh, Metagross, an old favorite ^_^
THE bulky steel to use and, of course, a solid check to most vgc dragons, I personally find Metagross to be one of those pokemon that is a real game changer, particularly when those stupid Swagger Cresselias started gaining popularity. Metagross has always been a popular choice for a lot of vgc teams, and it isn't hard to see why - massive base stats, great STABs, only two weaknesses, sacred ability that shrugs off Icy Wind and Intimidates, huge movepool featuring elemental punches and priority... the list goes on. It is one of the few pokemon that can check Latios without the risk of being fragged by Draco Meteor and then still be able to handle a large number of common partners to the thing, such as Hitmontop.
The introduction of the Therians to vgc has allowed Metagross to shine a bit more over its more recent rival Scizor, courtesy of its higher bulk, immunity to Intimidate and access to Ice Punch. I can't really say that Metagross is definitely better, or more popular, than Scizor, but Metagross is one of those pokemon that will always be around, and will always be dangerous.
Metagross has a fair few viable teammates - because it is one of the best counters to Tyranitar, it can form the 'weak against TTar + strong against TTar' combo (if you don't know what that is, it speaks for itself), which means it likes to pair up with stuff like Thundurus, Latios, Cresselia etc. Thundurus and Cresselia are particular favorites since they can control opponent's speeds, making it easier for Metagross to do damage.
Metagross's huge bulk means true counters aren't that easy to come across - even Garchomp is beaten if Metagross has a Life Orb or Steel Gem. Heatran is one of the best counters, being able to outspeed the 'Gross, though it needs Fire Blast or Overheat to be guaranteed the KO - and even then, if Metagross is somehow faster, it can really dent Heatran with Earthquake. Gastrodon is another good counter, since Metagross cannot OHKO it, but Gastrodon can with Ground Gem Earth Power, though it really needs to pay close attention to Metagross's partner. The best is Landorus-T, holding Life Orb or Ground Gem, because it will definitely OHKO Metagross with Earthquake, even with the spread multiplier on, which is helped by the fact that Metagross rarely carries Shuca Berry.
My current favorite set is not the usual. It was used by RubeNCB in the UK nationals last year, with a few tweaks:
Metagross @ Lum Berry
Adamant: 252 HP / 252 Atk / 4 Spe
Trait: Clear Body
-Earthquake
-Ice Punch
-Bullet Punch
-Protect
I like this set a lot because it really helps against a lot of things in the current metagame - Earthquake as a great spread move and to deal with enemy 'Grosses, Ice Punch for the Therians, and Bullet Punch because it's great priority. Not much else to say.
Obviously there are sets that use Metagross's strong STAB options, but this set works really well in the current Metagame.