Having actuall living conditions in mind I would go from a classic cyclist point of view with central europe.
US, Scandinavia, Asia and South America: no offense. There are great places. But:
a spot where you can ride a roadbike, a mountainbike, maybe some gravel kind of stuff if you wear a big mustache, having no car so that you need a good infrastructure, some good restaurants and things like that and a variety of routes, it just can be central Europe.
Freiburg im Breisgau in Germany is a real good spot. Some WT Racers live and trains there. The town is old, nice, full of students, in the summer a lot of sun and warm. In the winter snow. You can ride from the centre of Freiburg through the Schwarzwald. A really nice forrest with a lot of hills. Or you can go there an hike, ski whatever. With a train you are in no time in the Alps with all its iconic climbs.
If you like more sea, I would vote for Nice or San Remo. Sea in front of you, hills and Alps in your backyard. Nice more posh, San Remo more long in the tooth. Really good food, a lot of sunshine, a lot of hills, good infrastructure but not many flat roads without traffic.
Someting like this.
If I just had to vote for a city for MTB I would go for Vancouver, Canada or Portland, Oregon.