It's going to be difficult to continue body-buildinig (seriously) during the rugby seasons. It's pretty hard to attend practises and play one game a week and still incorporate the muscle stress/recover periods that a dedicated bodybuilding program requires. It's fine for the off-season, but once you actually start playing -- no. As for which to choose -- do you prefer team-type activities or individual ones? Rugby is a team sport through and through, while bodybuilding is about as pure an "individual" activity as you can get.