I pondered these two very closely as well, along with the Mits HD1000. Reading the reviews on the Samsung I chose it and am happy (after a false start with a bad unit).
To advise anyone else is tricky. Little to no pro reviews AFAIK
on the BenQ but several happy users it seems. OTOH most people report that they are happy no matter what they buy. This is either (a) True all the time or (b) people justify their purchases even if disappointed.
Sammy OTOH had loads of pro reviews, and they all said pretty much the same thing, so PQ was assured. (even if QC was not!)
I think the Sammy projects very nicely and the colors are indeed superb. I may have to get a brighter screen but I haven't played with it enough yet. Also I will be painting the room dark first then decide on the screen; there is some reflection off light walls and moldings right now. I also need to upgrade my DVD player. Have not watched any tv content on it yet.
If you will forgive my playing armchair psychologist for a bit then I read between your lines to think you actually want
the Samsung. (want, vs will prefer, ok?). I could be wrong of course.
Another thing that steered my away from the BenQ was the LCD vs DLP thing. I too had a 4805 and was happy with it. I figured, better the devil known than the devil unknown. This is, of course, purely personal and as far from a logical explanation as you could get.
Finally, to repeat what many here have said... any PJ in this price range (and above, of course) today will deliver satisfaction in spades, it seems. Just read all the threads; there doesn't seem to be a loser in the bunch. Go with what you think will make you feel good about your decision. Non-PQ features such as looks, brand name, pride of ownership, etc cannot justify a purchase but we need to accept that it plays a part anyway.
Good luck and let us know what you decide.