I've been to Heavenly, Squaw Valley, and Kirkwood at the end of March/early April three times and enjoyed each trip.
Kirkwood has the highest elevation and coolest temps. so there is less slush factor. I didn't like the mt. (runs are short/steep, then too flat half-way down. Base facilities were poor also.
Squaw has fantastic steep terrain that is more manageable with corn/soft snow. On a warm day though, too much of the mt. becomes mashed potatoes soft. I suggest an early start and check out Granite Chief or K-27 peaks. Avoid Squaw on the weekends unless you want to maximize babe watching, drinking, and tanning!
Ah...how Heavenly skiing can be at Heavenly in the Spring! Heavenly has Mott's Canyon & Killebrew Canyon for steeps. Gunbarrel for bumps. And perfectly spaced Douglas Fir trees for shaded snow off the groomed highways on any part of the mountan. Off the Skyline trail on the CA side is one of the best glades I have ever skied. Cool looking stumpy trees, small dropoffs and easy acces back to the Skyline Express quad. Check it out! The bar-be-ques, beer and babe-watching is just as good as the action at Squaw too!
All in all, Tahoe is great in the Spring! Enjoy!