Jim's advice and comments are worth following. I'll add a slight caveat. Unless you are very adventurous (i.e., willing to enter a gate that leads to who knows where), you may find yourself on limited terrain on either mountain. I would agree that Snowbird has a greater variety of long groomed trails compared to Alta, but you do have to know how to get to them. Maybe it just me, but whenever I go to Snowbird without a guide, I seem to end up on the same trails which seem to be connected by a number of cat rails that can feel, well, hazardous. When I have ventured unguided on either mountain, I seem to find myself getting 'cliffed-out' more frequently at Snowbird. I have been going to Alta on weekly trips for over twenty years and know the area well. When the snow is good, my crew feels that there is no reason to leave Alta. When the snow is not great my crew feels that we know where to find decent snow at Alta, so there is no reason to leave Alta. YMMV. Personally, I would like to learn Snowbird better (
@Jim Kenney : I hope that we can connect this winter!). The main message is that you will have more fun at either mountain if you can find someone to show you around.