A fresh turkey definitely produces better results. The texture of the white meat seems to be degraded if the bird is frozen.
Chris
PS: Being on my own these days, I don't actually buy either. I'm just recalling the turkeys that other people used to serve me on Christmas Day. (I usually buy cooked, sliced turkey breast and just heat it in the oven. Last year I bought one of those ready-stuffed frozen turkey joints but, on Christmas Day, I couldn't be bothered to cook it. So it was Findus lasagne for Christmas lunch in my house! Bah, humbug! Scrooge rules, OK?!)