Difficult choices in ColoradoI'll chime in with a few opinions. The summit county areas get heavy traffic on weekends from Denver. Vail/BC, being a bit further away and over a 2nd mtn. pass, and being more expensive, get a lot less pressure. So, if you are going on a weekend I'd definitely steer to wards Vail.
I'm a card-carrying member of the "i don't like Keystone" club. This attitude goes way back to the days that they told untruths about their conditions (okay, they flat out lied). But, the mountain does offer some good skiing. I'd recommend you ski Keystone for one day out of a multi day trip to Summit county. Experience it that way and you won't feel stuck if you don't like it. A LOT of people that I've talked to really like Keystone.
Breckenridge is one of my favorite mountains and the town is great. But, it took me a good many days to get to where I liked the mountain. It's one of the trickier mountains to 'get to know'. Skiing with somebody who knows where to ski on the mountain and when is a huge plus. This is of course true on all mountains, but I find it particularly relevant with Breck.
I 2nd the opinions already expressed about Beaver Creek. This is a nice tidy package of a ski area. Great skiing, easy to get around, easy to stay connected with your group.
Vail is just plain king-daddy. I don't like the town much. Paying to park & walk really sticks in my craw. But, once you get on the mountain it is just a dream If only we could get the star trek transporter to exist, this would be one of my favorite 'beam me ups'.
The shuttle systems around vail and around summit county are all excellent. Transportation shouldn't be a big issue.
Lodging is a bit tough (as in expensive) about anywhere. Vail / BC are going to be more expensive than Summit county as a rule. Shop the various property management companies and see what you can find. VRBO is good to look at.
Good luck and I hope your trip is the best!