InfamouslyJonesMy pick would be Alta/Snowbird.
Shuttle to the mountain is prime and fast and crowds are a lot smaller than at Squaw.
With that said - pitching a tent could be trouble if they are doing any avy mitigation. If they arent - then LCC could offer some prime camping spots. Just beware - there is a possibility the resorts will go into interlodge and you would not be allowed outside of the buildings - in which case find a bench or couch and crash for the night.
I think you need to base your decision on this type of information. Do as much research as you can.
I lived in Tahoe for half a decade and skied Squaw everyday. The terrain is nuts, super steep with lots of features. Put it this way, I now ski Mammoth 40 days a year as a weekender, and I love Mammoth, but I REALLY miss Squaw. Snowbird and Alta are sick too, great terrain, although I would say not QUITE as crazy as Squaw, and lots of snow. You are probably more likely to get deep light pow at Snowbird or Alta, but you never know. Even if you don't get pow at Squaw you might get some nice slush in March, and Squaw is a great slush mountain. Squalpine and Alta/Bird are two of the best spots in the country, so skiing wise you really can't go wrong. You might choose Utah and have it be dumping at Squaw, or vice versa, planning this far ahead you really don't know. If you like steep terrain and deep snow either location blows the doors off of Vail/Breck/basin, although I love Abasin.
When I lived in Tahoe the bus system was not all that great, but I left in 2004 so things might well have changed. I don't know what the situation is with camping, so I would do some research. I can't speak about the bus system in Utah, whenever I have gone to Alta/Bird I have stayed in Little Cottonwood near the resort.
Skiing wise you are choosing between two of the best locations in the U.S. Going to Mammoth 2-3 weekends a month means I have to spend about 500 a month on a ski lease, which ends up being 3000 a year since our groups rents a condo from Nov 20 to May 20. Because of that, I don't have a large travel budget. I should get to Squaw this year as one of my old buddies has a place there now and I can stay for free. I would like to go back to LCC, I have skied tons of pow on every trip there.
Seriously though, look into those details. Mammoth has had a pretty good season so far, not epic but pretty good. I think some of the snow at Mammoth has been rain at Squaw, but this storm might have set up the base. I don't know what kind of season Utah is having. But the most important thing is to look up the details of camping, that can make or break the trip. I know people who camp at Mammoth, but they don't tend to do so until May. Skiing wise both places are awesome, but you really need to pick the destination that is most feasible for what you are doing.