i used to work for Vitamin SHoppe, and we always had complaints about prolab's products. The creatine was maiking people sick, and other such things like this came up. That has made me very leary of prolab. I will not try anything of their's, unless it is highly recomended by someone I know and trust.
Out od the choices given, I chose myoplex Mass. It has worked very well for anyone I have recommended it to. However, I feel the best weight gainers are the ones you make your self. That way you know exactly what is going into it, and you control the amounts of what you want.