Methinks the better speakers should be on the side wall. Those are the ones that will receive discrete signals during 6.1 material, whereas the rear speakers will be given the same signal, and most of the time, it's just ambient sounds, although sometimes it is actual sounds, i.e., arrows whipping past from Gladiator. The sides will produce much more sound information than the rears, so make the sides the better speakers.
Can't answer your question about the speaker brands, though. Much more knowledgeable people on this forum can do that.
cheers,
supervij