For the weekend days I would stay away from Squaw or Alpine. Both of those mountains have horrible parking situations, and it can sometimes take up to an hour to get there once you turn off I-80 at Truckee.
Kirkwood is a good bet for the weekend. I was there last President's Day (and will be again this year), and it was very uncrowded, even on the holiday Monday. I asked a couple of locals about this and apparently, a lot of the season pass holders at Kirkwood have mid-week and non-holiday passes only. I have also heard this before I went, that Kirkwood can actually be less corwded on weekends than weekdays.
Of the other Tahoe areas I have skied at :
Northstar - not to impressed with the mountain. It was very crowded the day I was there, the Sunday after X-mas, and took about an hour to take the three lifts to the top of the mountain.
Sugar Bowl - Terrain looked impressive, even though most of the runs are short. Unfortunatly, I was not able to ski most of it as they were going through a freeze/thaw cycle that left the mountain in a solid sheet of ice. It was about as crowded as Northstar, just fewer lifts to the top.
For the most part, when I go to Tahoe it is for a long weekend, and I ususally end up skiing at Squaw if I can wake up in time to avoid the traffic. A note about Squaw though. If you are there during a storm and it does not look like the winds are going to die down, DON'T GO! Other than KT-22 and a couple other intermediate chairs, most of the lifts will not open. Despite this fact, millions of people will still head there, crowding up the base area quite a bit. Also, don't be fooled by all the hype ski magazines put into the KT-22 area. There are chairs at squaw that are less crowded, get you to better terrain, keep you out of the squallywood highway at the base, and are higher on the mountain (better snow). Find a local to show you around.