Having lived in various parts of the country and as one who enjoys seasonal change, I am of the opinion that Metro Denver offers the best climate in the U.S. Though the intense sunshine can produce significant summer heat, the low humidity and high elevation allow the air to cool rapidly during the night. Just sitting in the shade on a hot summer day offers significant relief and overnight temperatures generally fall into the fifties (F). Mornings are pleasantly cool (if not chilly) and summer evenings are mild as the sun drops behind the Rockies.
Though many Americans believe that Denver is covered with snow for nine months of the year (it can actually snow in the city anytime from September to May), winters are rather mild when compared to the Upper Midwest and Northeast. Again, the abundant sunshine, dry air and high elevation produce comfortable daytime temperatures, augmented at times by downsloping winds (chinooks); for example, the average high temperature in late January is in the forties, compared with the twenties in Chicago. Radiation cooling often produces overnight lows in the teens but the temperature rebounds quickly under dry, sunny skies; winter snow is, of course, common but generally evaporates within a few days.
The downside of Denver's climate (if there is one) is the propensity for heavy, upslope snowstorms in March and April, just as flowers are appearing and trees are leafing out. But the cool summer nights and mild winter days more than compensate.
