I prefer Keystone over Copper personally. But the cool thing for you since your coming on a trip, is the free cat at Copper. Others will say that Copper is hands down better then Keystone... Personal preferences
I personally enjoy Vail and Beaver Creek over all of the other "local" mtns
"When I do good, I feel good; when I do bad, I feel bad. Thatís my religion." - Abraham Lincoln
Copper has better terrain, better snowfall, doesn't sit in the shade 90% of the time, better vibe, free cat, better snowfall, park flow allows for a 45 minute lap, mid week isn't crowded with dumbasses, better snowfall, and did I mention better snowfall.
I think you meant 4-5 minute laps. I too think Copper has much better terrain than Keystone. It's also nice that the mountain is naturally divided by ability level. So you don't have a lot of intermingling with riders/skiers of different ability levels on the slopes. About the only place where that happens is the base areas bottom 1/4 of the mountain. Basically where everyone has to go at the end of the day. It'll be less crowded than Keystone too for sure. As BA mentioned Copper gets more snow fall too. The most in Summit County with the exception of A-Basin.
just pick a cheap place to stay and get a 4x4 and go to all of the mountains in the area im gonna be there during january staying between keystone and brecken, but i'll probably hit up copper, brecken and keystone, so really it doesnt matter much unless you dont have a 4x4. Everyone complains about every mountain out there i suggest you hit them all up and decide for yourself which is better. Really its mostly your individual taste, and yah copper will be less crowded if you really hate waiting at the lifts, plus keystone has the night skiing thing which is always good if your still not tired as hell after a full days riding.