Abasin does get really crowded on the weekend AFTER all the other resorts close. If breck/key/vail are still open, A basin is pretty much ALWAYS empty.
Case in point, Brecks "26inch" day. I showed up at breck for first chair, skied 3 laps with 20 minute lift lines, left at 11 and came to A basin which reported 18. A basin was completely empty and so much better.
So, if everywhere else is open still with this late easter, I would go to Breck on weekdays and a basin on teh weekend to avoid the crowds as best as possible. I dont think I've gone to breck on a Fri/Sat/Sun this entire year.
A basin has a lot of legit terrain if you know where to look. Pali chair and face has a lot, check out runs like turbo and the alleys for the best steeps inbounds in Summit (unless you count lake chutes at breck...but those are only 500vert). Montezuma bowl has some great terrain too. The trees off to the far skiers left are good. Go all the way past them and theres always good snow, never touched. Also, the main bowl zone has a few decent cliffs, espeicially if you gar skiers right.
Breck is basically only good for park. Dont say I dont know the mountain, Ive given it way too many good days and know of lots of "secret spots," they all suck and are flat. Breck is a blast for park, but other than that....meh.