http://en.wikipedia.org/wiki/Magus_%28comics%29

&

http://en.wikipedia.org/wiki/Thanos

Vs

http://www.geocities.com/dcnw0/Legion/Villains/omen.gif

Can't find any good links on Omen and Prophet, but Omen was said to be even MORE powerful than Great Darkness Saga Darkseid. And Prophet took down the Legion Of Super-Heroes by himself. Prophet works for Omen, iirc.