Go as big as you can, i.e. 50" for 6', 56+" for 8', 60+" for 10', and 70+" for 12' viewing.
The bigger the screen, the more difference you see between DVD and Blu-ray. If you are just buying a 42" to watch from 12', you might as well not bother with Blu-ray, because your eyes won't resolve more than 480p resolution.
Well I own SXRD and I'm generally pleased with it considering price. I like to watch in a somewhat dark room, so I couldn't stand LCD grey haze on dark portions anymore. I also have windows in the room and screen reflections bother me, so I wouldn't buy a plasma either.
I did look at LCDs again when I got fed up with old HDTV. My opinion was that the 47" Sony and Samsung had rather poor black levels. Without playing with settings, the Sharp LCDs sure seemed to have a lot of artifacts in the picture. I suppose if forced to choose between only LCD or plasma, I might go plasma just because I know I hated watching movies on my LCD whenever the room wasn't bright. I've found that SXRD blacks aren't as great as I had read they were, so black level would still be my major buying concern on any TV. Honestly if you can stand screen reflections, don't need a flat panel, and are okay with the extra weight - CRT rear projection still might be better than anything else.