Least crowded I 70 resorts

Your best bet is probably still Copper, it can be rough but it's never THAT rough.

Winter Park is the same story even though it's not RIGHT off I70 travel time should be similar if you are coming up from Denver.

Not an I70 resort but Eldora has a really fun setup right now and never has lines

This is from exactly a year ago (when I worked at Eldora)

May/may not be struggling with snow amounts currently, but the park can be tons of fun to lap and usually is not crowded at all (especially compared to summit / i70)

Considering both passes depends on the day mostly. Beaver Creek is usually not too busy(minimal park skiing). Vail is only busy during storm cycles and pow days on the weekends(no parking left by 9 am)Some other days can get kinda busy. Size matters(golden peak usually not busy). Weekdays are pre much dead for lines. Copper can have some great lifts without lines even on the weekends(Resolution, Alpine, Bee, Backside lifts). Breck is a crapshoot. Same with keystone(both with decent parks give or take some cuts each year). Loveland and Abasin are similar in terms of crowds which is not much(some rails and a couple of small jumps). Winter Park can be off and on. Pow days there seem to be busy on weekdays and weekends. The place can see lines at some chairs similar to breck. So in conclusion, if you ski on the weekends, avoid(from mid-December to mid-march) Breck, Keystone, Winter Park(pow days), and Vail(pow days). Places that can still offer lift line free access are Copper, Abasin/Loveland, Breck(only on the E, 6, and imperial chairs), Beaver Creek, and Vail during drier periods and the lifts which access the bowls(soften by 1 pm in 30+ degree weather). One benefit from Beaver Creek is how far away it is from Denver along with Vail usually receiving more snow on pow days which take place west of the Continental Divide. Even a 1-inch difference will have all the pow-slaying dads cling to vail because of the back bowls. Its also been a while until this year since I rode the resorts on the Ikon(which used to be the colorado pass I believe).