I feed live as my supply dictates. When I don't have sufficient live pinkies/fuzzies each week, I feed from my stash of frozen. I haven't yet experienced any problems with snakes refusing either type of meal after sampling the other, specifically live.
I also feed all my snakes with tongs and generally wait for them to grab the meal. Hence, whether it's live or dead, they see a pinky hanging in mid air waiting to be eaten. That may or may not be the difference in my experiences.
So far, knock on wood, almost all of my snakes have been aggressive eaters, and have had only one or two picky starters that a few meals worth of brained pinkies fixed rather quickly.
D80