Both, I enjoy the process of building, so following instructions. But then it's done and boring. I.e. LEGO supercars sets are nice, they're so nice until you marriage chassis with drivetrain - you can play with all the gears and see them, after the marriage it's just boring. So now I'm working more towards reusing parts and building things of my own.

Edit: LEGO Architecture Set (not sure if they still make it) is super nice for building random stuff - it's a set of pure white bricks, super fun.