I honestly canot stand LCDs for TV viewing, and much prefer Plasmas and DLPs. As far as showroom viewing, just make sure everything is set to defaults across the board to level the playing field. You would be surprised to see how they jack up brightness and color on sets they want to move.
Even the defaults are not how one would want to judge a set. Manufacturers jack up the brightness and color temp out of the box. Bright and blue looks good under glaring florescents, but not in a living room. If you do want to try to compare sets on a showroom floor, the your best bet is to set them to "Movie" and "Warm", but even that isn't going to have the black and white levels set correctly.
Really, side-by-side compares on the fly can't be done to gather enough info to reliably pick one set over another in a showroom. It's best to read up on actual benchmarks tests online (preferably done by the same reviewer/site), and pick out the display which meets most of your wants, and has the least misses on things which you think will bug you (because no set is perfect).
