Hubby and I have always found the beds on Carnival ships surprisingly comfortable. I say "surprisingly" because we have the twin beds pushed together to make a king-sized bed....but obviously there is that "seam/gap/crack" in the middle. I ALWAYS think its going to bother me, and I ALWAYS forget completely about it and sleep wonderfully.
Best thing about the beds on Carnival: I DON'T HAVE TO MAKE THEM UP!!!!