Rugby vs RowingWatch
My mate was part of the rowing squad at cambridge (his rowing abilities was the only reason he got in actually as he got 3 B's) and said it was brutal socially, they're so focussed on the varsity boat race that boozing/having fun is a big no no. I'm guessing rugby would be more laid back.
Rowing you tend to form better actual friendships - cos it's 8 of you training together all the time; but if you're just up for a night out every week then probably go for rugby. Most college rugby squads have a night out every week