Estimate from a mix of 1st and 2nd hand info:
Places with lots of intermediate terrain, but probably very crowded if conditions are good: Killington, Mt. Snow, Stratton, Okemo, Stowe
Places with good intermediate terrain and might be a little less crowded then first group because they are farther from civilization or overshadowed by other areas: Sunday River, Jay Peak, Pico, Sugarloaf, Smugglers Notch, Sugarbush North, Wildcat/Black
Smaller places with a fair amount of int terrain and possibly smaller holiday crowds because they aren't marquee names: Burke, Bolton Valley, Bromley
I've probably left off a few other good choices. All the above have a possibility of frostbite weather since they are in VT, NH or ME and that risk comes with the territory in late Dec. If the weather is not so great for skiing in early Dec it can work in your favor by reducing crowds. The bad publicity in the press can diminish holiday bookings making even some of the popular places decent, especially if there is a good snowmaking stretch for 3 or 4 days just before your visit.