Winter Park is nearly an hour's commute from the Summit Co. area, so I would also opt for one of the Vail Resorts passes. If I was skiing for that long, I would spend a few more $$ and get a pass that lets you ski at Vail and Beaver Creek also. The added variety would be well worth the few extra $$. My guess is that you'll end up spending the majority of your days at Breck or Vail.
A-Basin is a relatively small ski area, so it lacks variety. Keystone is my least favorite place to ski in that area. I find it to be mostly wide groomers packed with 60 mph. snowboarders. They also seem to have the worst snow cover if conditions are marginal. Breck is big, crowded, but has lots of variety. Vail is even bigger, and is my favorite ski mountain in the area. The bowls, if they have enough snow, can bring a smile to your face all day.
For several years, we've bought the WP/Copper passes in lieu of the Vail Resort passes. We ski WP (mostly Mary Jane side) about 2:1 over Copper. Because we make many daytrips from the Front Range, WP is appealing due to being able to avoid the Eisenhower Tunnel. I've spent hours on I-25 trying to get home from Summit Co. on a Sunday evening when traffic was stopped at the tunnel. If you're staying in SC, you won't have to worry about that issue even if jaunting over to WP, as you'll be going against the major traffic flow.
Enjoy your stay!