Copper is probably the best. It's a huge mountain with a reasonable number of intermediate trails. It's on the scale of Vail. It gets a lot more snow than Loveland or A-basin. I promise you wouldn't get bored.
Loveland would be my next choice. They have quite a few intermediate trails. If you looking for some cheap skiing that is close to home Loveland would be my choice. Lastly, A-basin is an expert's mountain. It's not worth going there if you don't ski advanced and expert terrain. Maybe a third of the mountain is blue and thats mostly groomed steeps. It is also windy up there. The terrain under Pali is the best part of the mountain. Only if you want to bump up to the next level would I go with A-basin. It has some other things going for it, it's cheap and it's close.