I dunno, I guess out of these choices, it would be either Ducky or Little Foot. Ducky because of her pretty, bright blue eyes, Little Foot because he has a slender, yet kid-like physique. So I'm not voting, sorry.
Now if the question said something along the lines of: "Which LBT character in all of the series do you think is the most attractive?" I would say Pterano. He has some very elegant physical features, like his crest, beak, wings, etc. I mean I guess the creators made his character physically like that to symbolize his vainity. But of course we find out in the end that he's just insecure. :^.^: