How to do a successful demo day:
1. Find a set of runs you are comfortable with that includes a flat section, a steep section, some crud, some ice, some groomed....anything you think you'll encounter on a regular basis (or whatever conditions you're buying a specialty ski for). Take each ski on the same run routine and at the same speeds for an accurate comparison between models.
2. On a smooth section, try riding the ski with your weight forward, centered, and back to see how it will react to unexpected weight changes. Which is it most comfortable with? If your weight is forward and the front of the ski just smushes out from underneath you, the tip is too soft. If it zips into turns without you, it's either too stiff in the tip, or has too much sidecut for you. With your weight back, does it just go straight? The tail's too stiff. Skids out? Too soft. Also try a progression from smeared, skidded turns to seriously edged, purely carved turns....which type of turn does it feel most comfortable in? If it tends to skip out of turns when edged, it's too soft for you. If it balks during the progression, it's probably too stiff.
A ski that's "snappy" or "lively" will come alive under your feet. It will want to turn. If you pressure it, it will "snap" out of the turn (a seriously scary feeling the first time) and want to roll immediately into the next turn. Think Porsche.
A ski that's "damp" will motor smoothly into and out of turns. It will feel like driving a Cadillac, smooth and mellow.
A "powerful" ski may also feel "damp" or "snappy", think Hummer or Corvette.
All of these things you'll just know when you feel them the first time. Most people will tell you they're not a good enough skier to know the difference between skis. All that says to me is they've never tried multiple pairs of skis on the same day. You WILL know the difference. It doesn't matter how others rate or describe the skis. It only matters how they feel to YOU.
I also wouldn't really make a list. I've found when I've done that the skis I wanted weren't available or were the wrong length, etc. Don't limit yourself to any particular maufacturers or models...try EVERYTHING they have in your size as well as 1 size longer and 1 size shorter. My biggest WOW's have come on skis I hadn't planned to try, in sizes I never would have considered.
That said, most maufacturers have a general "feel" throughout their line (my impressions, YMMV):
Volkl - snappy and powerful, loves speed, race oriented
Atomic - burly, powerful, and precise with stiff tails, requires speed, race oriented
Fisher - powerful and precise, loves speed, race oriented
K2 - damp yet playful, easy going, fun oriented
Rossignol - very damp, smooth and predictable
Salomon - snappy and light, fun and energetic
Volant - very smooth and damp, stable and powerful
Blizzard - light and snappy