Big Cottonwood is the least crowded - Brighton/Solitude
Little Cottonwood is always the most crowded. Alta/Snowbird
Park City isn't worth it unless you're a huge park rat and need the "ski town" vibe - also usually crowded.
Powder Mountain/Snowbasin aren't worth the drive unless it's snowed a decent amount in the past 3 or 4 days.
Even a crowded day in Utah is really nothing, the last time I've actually waited in line was at the very end of April last year, pow day, all other resorts was closed. Waited in the tram line for 5 minutes.