Monaco can be more defensive, or more attacking, he's not one dimensional that way. Igor can't play defense. His game is to go for everything on the forehand, and misses half the time. He has nothing else to rely on, and it isn't like he can tone it down and stay in rallies, since he has a liability of a backhand that gets attacked a lot, and his forehand is so loopy he has a hard time defending on that side consistently. Juan is more solid in all departments.
Juan is far steadier than Igor but he's still very one-dimensional. Give him a variety angles, pace, spin and bring him to net and he's fucked [eg. Ljuby at IW].