I would say Steamboat. It's a real ski town, fairly remote, and doesn't suffer from the day tripping hordes that come up from Denver like Copper does. It is also not a very steep mountain (though it does have some steeps), but still has uality free ride terrain. The pipe is decent not so sure about the terrain park. It is also the only game in town.
Copper is in Summit County, so Keystone, Breck, A-Basin, Loveland are all close by. Vail is just over the pass to the West of Copper, so it is also close by. So if you want a bit more variety, Copper will offer it up to you. Just expect large crowds on weekends. It gets crazy some days. It's also much easier to get to the Denver metro from Summit. You probably won't have to do it often, but most people eventually have to make a trip to the airport, or down to the Metro to get something that is just not available in the mountains. It's a 80 minute drive (or less) from Summit vs about 3 hours from Steamboat.