Alpine and Sugarbowl both have challenging terrain if you look in the right place, can be quiet on weekdays, and have staffs so friendly you may think you're at Disneyland.
Although friends who have not skied it recently tend to dis Northstar, it has real charms, too. The front side is mostly tame and often crowded. All runs on the backside are marked black, though, which scares people away and keeps the lift lines short to nonexistent. No bowls back there but long runs, good vertical, and nicely spaced glades that get little traffic. Ski Alpine while it's storming and head for the trees at Northstar the day after.