Actually, I've heard nothing but good reviews of the Behringers, by folks that I trust... and believe me, I subscribe to the "Behringer gear is crap" school of music. :)

Read many articles on mixing and "critical listening". Go to a big music store that has a listening room with all of these makes of monitor, and bring a bunch of music that you know really well. Trust your ears. Listen to the *really* expensive ones as well as the ones you can afford. Buy what your ears tell you to.