Squaw and Alpine for serious stuff. Skip Northstar...it is a mall next a pedestrian ski resort. It is very much like Vermont mountain, with trails carved through trees, whereas Squaw doesn't even have designated "blue" or "black" trails...they just mark the lifts. Hell, Squaw doesn't even have many "trails." It's all bowls, chutes, and wide open fun. Backside of Alpine is great fun for steeps. Big, wide open bowls on the front side.
Do Alpine and Squaw first...you'll be convinced you've kicked ass. Then make the time to get down to Kirkwood. You won't be able to do it all in a day, but go for it. Do the #4 chair to the wave. Do the chutes if you have the balls. Sentinel Bowl has some great steep glades. Even the greens are fun as hell if you need a brief break.
If you can't make it to Kirkwood, I'd recommend Sugarbowl as your third choice. Chutes, steeps, and a drive through the Donner Pass for history. Don't bother with Northstar unless you're trying to impress a fiancÚ or something. It's all hype, very expensive, but nothing will challenge you. Other than your credit card bill.