I'm sure this doesn't even crack top 10, but Minneapolis is very lively in the SUMMER during happy hour. Not as lively as a weekend night but pretty hopping for a sleepy Midwestern town. I'd imagine the most lively would be:
NYC
Chicago
Miami
Philly
San Fran
Hard-working cities with decent weather (seasonal) and more party-oriented. I excluded LA because I biasedly think people in LA never work and just party all the time.