There are no linebackers in rugby!
It really depends on what league you're playing in. If you're talking about high school and college, then bulk is better because the running game is a lot more important in those leagues. However, in the NFL, mike/middle linebackers are starting to realize that TEs like Graham/Gronko/Hernandez are playing the middle of the field. Mike Linebackers in the NFL have to be fast and big.
I'd say bulk but you still need speed. Look at tom wart(ohio buckeyes) he soon is going to be drafted byvthe nfl. But he has a amazing speed for a player his size.
