Well MLcad is a more cad approuch to Lego Designing. But for as i have know MLCad always had 4 windows, and the forth window is the 3D window if you want it for the 3D view. I prefer MLCad but thats just because i've been working with MLCad for years now and i know that program inside out. If there comes a day i cant use it anymore because of driver problems or what ever, i will need to try out LDD and it would probably still work fine ^^