At this point I would recommend the BenQ. This is mainly from my extremely bad experience with the 1633s and what I have heard from other LiteOn ppl that have been disappointed with the 1693s.
I don't have any experience with the newer BenQ 1640, but I do have a friend with the 1620, which I gotta tell you I love.
I have been vacillating between the BenQ 1620 pro, the LG 4163B and the NEC 3520a...
So I kinda in the same boat you are in. Personally considering the BenQ 1620 experience I have had with my friend and the experience I have had with the 1633s, I would go with the BenQ 1640.
Here is a link you might find useful:
xbit labs reviews on the LG and the BenQ:
BenQ Xbitlabs review
LG drive Review (xbitlabs)