There are a lot of cities that fit that description, but being the US, you're not going to find a lot of good options that have a decent overall quality of life, and aren't incredibly expensive.
The best metrics to look for IMO are:
- Bikability
- Usable public transportation (< 10 US cities have this)
- Good infrastructure / livability
- Green spaces / parks
That leaves only a few options, all of which are expensive, but still far better than any other alternative:
My top picks are:
- San Francisco / bay area
- Washington DC area
- Boston area
- Seattle area
I've lived in many of these places and can vouch for them.
I personally hate these below, because they're grimy / filthy, have a ton of cops, and are filled with podcasters, but they do have good public transportation and a few other redeemable things.
- NYC area
- Chicago area
- Philadelphia area