Sometimes I think the mask is the hardest equipment to chose. When I was in OW, people tried masks on me, and asked if they were comfortable. Ok...now...I have this "thing" on my face, looking through a fishbowl, and I can't breath out my nose. Is it comfortable???? NO!
The think to look for in a mask, besides sealing, is see if you can feel anyplace (other than the seal) that the mask is touching (ie. pushing up on the bottom of the nose, pressing against your brow). Purse your lips (like you had a snorkel or reg in your mouth) and make sure the skirt doesn't "cut" into your upper lip. Any pressure you feel in the store will become unbearable if you have it on for more than 10 minutes. When I first started diving, I had problems equalizing. Didn't realize it until I changed masks that my mask was pressing up on the bottom of my nose, and after a while, it hurt to much to pinch my nose to equalize.
Most of the time, you really don't know if a mask is right until you get it in the water. See what your Dive shop's exchange policy is. See if they will switch out the mask for you (still in very good condition, of course) as many times as it takes until you find one that works for you. I think most shops will exchange, as long as it isn't real beat up.
And, don't worry about what mask the employees use. Its always good to get someone's opinion, but what fits one person may not fit another. If you take care of it, a mask will last for YEARS. Could be the employee bought it 5 years ago, in another part of the world, and just fell in love with it!
Hope this helps. And good luck!!!