I play with two different armies, one guy that's just starting out and another that is a veteran.
When I last played the veteran, he had a few squads of warriors, he had some immortals with tesla, a monolith, a lord or possibly an overlord (can't remember which), some of those wraiths with all the tentacles, and I can't remember what else, but I think he had some vehicles. it's been a minute since I last played him.
The newer player runs: An Overlord with staff of light, 12 warriors, 3 scarabs, 5 immortals with gauss weapons, a monolith, and both of the c'tan shard variants (deceiver and nightbringer).
He just got the monolith and the c'tan shards, so I haven't played those yet, but I'm going to be bringing lots of AP and more suits than i previously had against necrons. I don't think either of them ran/run formations, but with the decurion buffs it's really only a matter of time. And I'm not sure how I feel about those god shard dudes.
Thanks for the help!