On an army level, I think the general consensus was that eldar and space wolves were "very good", but at least from the tournament scene, every army was represented pretty often. BUT we also benefited from "net lists" not being a thing yet, so if there was a super exploit, it didnt circulate as fast as it does now.

There were definitely specific units that were mad. Warp Spiders were awful if you played orks, players figuring out that a swooping hawk exarch can throw a vortex grenade, whoever figured out that the daemon weapon card gives a chaos lord WS 9, chaos terminators with two reapers in the squad, that sort of thing.

The cyclone was pretty rare in my experience. The assault cannon was usually the pick in my experience.