Winter is miserable in Utah unless you are obsessed with skiing. The inversion is horrible and everything is gray and sad. Spring and summer are the months I want to be in Utah. I would also throw in early fall as a maybe. Those are the times to go hiking, to lakes, camping in the mountains. Besides that mornings and evenings in a Utah summer are wonderful. The temperature drops when the sun goes down and it is perfect. The low humidity makes the heat bearable. Its hot in summer but not Las Vegas, Texas or Arizona hot.

Summer on the east coast, midwest and in the south is brutal. Waaaay to humid. I cannot even bear being outside. If you do go out even for 1 minute you are dripping in sweat. The heat does not drop when the sun goes down so there is no respite. Swimming and getting ice cream are the only things worth going outside for. Southern California is similar but the beach is there.

Fall in Utah is honestly not that great if you compare it to the East and Midwest. There is a much greater diversity of trees in those places that provide more beauty and the colors last longer because the elevation is lower. Days are nice and evenings are pleasant.

For me:
Winter- Southern States, California
Spring- Utah, Colorado, some Midwest- probably California
Summer- Utah, Colorado, Idaho, Montana, Northeast, Alaska, Great Lake states, Washington/Oregon if not raining
Fall- Midwest, East Coast

Hawaii- Any time
Wyoming- No time

I'll qualify this by saying if you are in St George then nearly everything I have said about Utah reverses.