These are the pros and cons I have personally experienced of both locations (slc-4 months, mammoth-3 months)
amazing weather, amazing park, cool surrounding area(tons of sights to see in the spring), crazy level of skiing and riding, main park is like a 3 min lap, south park is the best medium park anywhere
small town, need to make the drive to reno to fly, tahoe decently close, vons has free soup samples
good park but not as good as mammoth, close to major city w/ cheap housing, nearby urban stuff, airport, other mountains(with lifts) close
not quite as perfect weather as mammoth
not as much terrain as mammoth(the canyons/ little cottonwood canyon have this though)
Over all, I prefer Mammoth for its atmosphere and all around sickness, pc sometimes just gave me bad vibes for some reason, If I were you, I would also consider North Lake Tahoe because it is somewhere between the two, with lots of mountains, sick parks at alpine, squaw(in the spring)etc and also some sick natural terrain, all with a weather pattern somewhere in between Utah and Mammoth.