Best US City To Live In?

I'm a single forty year old man( keep being told that I look ten years younger.) My point is that I'm looking for a great city to live in that has a lot of singles, reasonable rent, and that has a good public transit system so I would not have to deal with the hassels of owning a car in a major city. I have lived in Conn, NYC, Boston, and now am living in Suburban Atlanta(It's ok here but everyone in the neigborhood is already married with kids. I really don't think fory is old if you don't look it and have never been married and don't have kids. I think NYC and Boston are great but don't want to shell out over 2,500 dollars per month

I'm really just looking for a nice, safe, and fun city that has a good public transit system and people that are easy to meet(the Atlanta suburbs can be pretty hard to meet people.) Most people already have a social circle and seem to be very set in thier ways.