Me:
Grew up in Utah Valley not SLC. Non-mormon. Only been to Denver once. Currently live on the East coast.
My thoughts:
1) SLC is a tad cheaper than Denver.
2) Public schools in Utah aren't great, which is/was driven by a couple factors from my perspective:
low aspirations of the students - most kids in utah just aren't aspiring to attend prestigious east coast colleges. This ends up setting the bar low. Any self-motivated individual can still succeed because there are plenty of AP and honors courses, etc. just like anywhere else. Having spent a decade on the east coast, I really enjoy the positive peer pressure that comes with being surrounded many other like-minded, driven individuals.
low value placed on education - there just isn't the same value placed on education for the sake of education that you'll find in other states. This is related the above and has the same negative effects.
lack of critical thought - this may be a bit more controversial and I'm sure the lurking Mormons will disagree, but Mormon culture almost inherently is devoid of critical thought. This affects utah's education system by really lowering the quality of teaching and participation in non science and math courses such as history, English, philosophy (if its even offered), economics etc.
low spending on education - like others have said there is a low per student public spending on education and there aren't a lot of private options either. That being said the athletic facilities at a lot of Utah schools are superb. This isn't surprising given the states priorities. Instead the spending effects the quality of instruction, class room size, pay of teachers, etc.
This last point really isn't a huge deal. Most studies (I can't cite any) show that spending and education achievement are not causally related. The other three above points certainly do matter though.
3) The school environment is not great for non-mormon children. It essentially boils down to being a non-mormon becomes another potentially point of "bullying". "Bullying" for lack of a better term is just a fact of growing up, but your children will have a de facto target on their backs. I had two siblings, one escaped unscathed, I had my moments and problematic people who hassled me for being non-mormon, and one sibling probably had the worst and likely has been affected long-term by the environment. Essentially your children will need other factors to counterbalance the non-mormon stigma, good lucks, popularity, athleticism, humor, etc. However, even if your kids can manage to beat their non-mormon stigma, no matter what they will be subjected to endless attempts to convert them.
4) For mormon's almost all social activities begin at and revolve around the church. For a non-mormon you are constantly out of the loop, subjected to awkward moments, and must decide to what degree you're willing to engage with their church for secular reasons. It's a bridge they'll have to cross.
Note again this is all specific to Utah Valley with 90%-95% mormons and not SLC. Also I wouldn't expect any single, childless, 20-something non-mormons in Utah to have any perspective on what it's like to raise a non-mormon family in Utah. There's an entirely different set of experiences that 20-something non-mormons wouldn't be exposed to in Utah. Lastly, most mormon's I know and grew up with are also completely oblivious to points 3 and 4. Even my closest friends who were generally the most open-minded people I grew up with were completely unaware of the experiences of a non-mormon growing up in Utah. It's just so far outside and beyond their "water" that they are completely clueless, at no real fault of their own.