Well it's a little too generic to say there's one perfect target, although I guess I'd probably go for shooting the solitaire. He's a deadly close combat monster, and dies pretty easily out of combat. Plus, even if you take 2 lascannons to take him down, it's worth it to keep him out of combat, and get rid of such an expensive IC.
Problems arise however when you're playing different armies, like Orks who would want to tie up the solitaire with grunts so they can gang up later. Basically, anything expensive is a prize