I haven't been EVERYWHERE, but Boulder is really hard to beat. It was the birthplace of the 7/11 team, which pretty much single-handedly introduced pro cycling to the United States. The terrain is almost a cycling cliche, the weather is incredibly benign, even in winter, and you will constantly see $3,000 mountain and road bikes on top of $2,000 cars. I never would have gotten into cycling if I had not moved to the area for other reasons.

I live closer to Golden, but things are similar. This was taken literally five miles from my house, and I live in "the city".