While my http://webpages.charter.net/tcrocker818/fam_ski.htm
page analyzes the snow appropriately, the other issue is that most managements start closing facilities by mid-April. This year may be especially bad with Easter so early.
Currently Mammoth plans to close Canyon/Eagle April 21. That will also include chairs 9&22. Plan on about 60% of terrain available unless it's a big year like 2005 or 2006 and they delay the Canyon/Eagle close.
Bachelor is worse. Powdr Corp management is cheap and Sunrise and Northwest will almost certainly be closed by then. Furthermore Bachelor also closes the mountain at 1:30 when in spring operation. Mammoth will start trimming hours in May, but I've found it by experience highly dependent on snow conditions. With good snow Mammoth will run full hours, vitually a certainty through end of April.
Whistler will have one mountain open late April and May after WSSF is over. Let's hope it's Whistler with the greater north exposure.
I like Squaw/Alpine skiing, but with the much lower altitude than Mammoth, it is common for the snow not to freeze overnight in spring and thus be much stickier. If you go to Tahoe, I think Kirkwood will still be open; your week might be their last.
Louise and Sunshine are pretty good about staying open if they have the snow. In a below average year Goat's Eye and frontside Louise are going to have some rocks by late April.
A-Basin will run everything but it's a smaller area than those above. The new Montezuma will make it bigger (haven't seen it, don't know how much) and Loveland is also still open to first of May, though with more variable exposure/snow than A-Basin.
Snowbird is still running most facilities, might shut Gad II or Mineral, in late April. Make sure they have not gone to weekend only operation as in May.
Long winded, but on balance I would probably vote for Mammoth or Whistler. Before Powdr Corp I would have recommended Bachelor.