The Epic is a great deal if you want to ski at Vail and Beaver Creek a lot and maybe throw in a visit to Tahoe too (Heavenly and Northstar). If you want to ski a lot in Summit County (Breckenridge, Keystone and Arapahoe Basin), with only a few days at Vail and BC, the Colorado pass is an even better deal. The Summit pass gives you Breck, Keystone and A-Basin and a reduced daily ticket fee at Vail/BC.
I'm not sure why you would ever buy a summit pass it's like an extra 50$ for the Colorado and the Colorado pass also included days at Northstar this year. Ski for one day at Vail/Bc or Northstar and you make up the difference