Generally, PCMR has the longest lines on Saturday. They sell a Utah Student Pass to all local kids for very cheap (about $100) and that is the day mom drives up from SLC & Provo and shops at the outlets while Jr. and his/her three buddies mob the place. Luckily, they mostly stick to the terrain parks, so the upper mountain/expert terrain is lighter in crowds. On sunday, mom & family are in church, so the the resort is relatively slow. Keep in mind that the high season can creat significant crowds no matter what day. That said, I can always find areas/lifts that have short/no lines on just about any day if you know how to work around the mountain.