I'm wondering if some of you experienced residents, runners to or travelers to Asia have an opinion as to which of these 3 cities (Bangkok, Shanghai or Beijing) would be the most interesting to visit?

We want to do a NW mileage run and we are willing to pay more to get out to one of these 3 destinations, because China and Thailand are the only two biggies we've missed in Asia so far.

Any opinions on which would be the most interesting city for a long weekend, for an active, adventurous mid 30's couple? Thanks!