Odin, Thor, Amora, Skurge, Loki (ok, technically not Asgardian, but IMO he counts), and early showings of Heimdall were as impressive as almost any Olympian. IIRC the Grand Vizier had some good showings too, and during JMS run, you show another high end sorcerer in the Asgardians.
Tyr also had a pretty even fight with Thor back in the day...better than most gods in any pantheon do. So, I'd say the 'named' Asgardians...the ones listed in the mythology books, are very much on par with the 'named' Olympians...heck, unnamed Asgardians have proved far more impressive than someone like Ares, save a few of his more recent appearances...though Baldur is kind of a mixed bag (at the end of the Simonson run, he was awesome, but he's been re-relegated to 'normal' Asgardian a lot since...
Odin, Hela, Karnilla and Thor seem to be their top levels
Who would be for the O, other than Zeus?