I only know of one national show that announces the judges beforehand, and that's Road to California - they list the judges on the entry form. For local shows, they may have only one judge, and hire the same judge each year. Depends on the show.
I have entered a lot of shows (it's addictive!), and while I know there are judges I felt liked my work better than others, it is far too much effort to keep track of their likes and dislikes. I try and make a quilt that I am happy with, do the best work I can, and hope for the best - when you work by hand, that's pretty much all you can do. For some shows, just being accepted is triumph enough.
There are some shows that cater to specific quilt categories. Quilt National, the quilt show at the Schweinfurth Museum in Auburn, NY, and a few others, look for the best art quilts. They would not be good choices for a traditional quilt - that's not to say you wouldn't get in, though. There are shows specifically for machine quilting.
Most national shows I've entered have had 2 or 3 judges, all of whom look at the quilt. Considering how many quilts they have to judge, I don't think they spend enough time to whip out a ruler and measure anything - good thing, because they'd find lots of mismeasured things on my quilts.
Janet