I think you all need to look at this as a continuum:
---> anorexic... skinny... fit... curvy... thick... full-figured... fat/obese ---->
It's not just "skinny" vs "curvy".... what a guy thinks when he says "curvy" is a body type like J.Lo or Salma Hayek whereas many plus-sized women consider "curvy" as the correct descriptive for themselves. These are words - they are interpreted in a number of different ways.
As an aside - the word "skinny" is just as unattractive as the word "fat".
You also need to remember that the "butterface" syndrome can often throw these out of whack. A guy will often prefer a thick girl with a pretty face than a fit girl with a butterface.