I was skiing midwinter snow on the upper part of big sky the last weekend this year. I was also riding the tram with no more than 4 other people in it every lap. If you don't like crowds go to Big Sky, but I think the terrain at Jackson and Alta may be a bit better.
alta is pretty good, they usualy get some really good snow still in the spring. big sky isnt bad, if you want a better park go to jackson over big sky, they are both kinda the same though. alta the best though, cuz u got snowbird right there too.