I don't think I have most or least favorites. I think it depends on the person the body part is attached to. But in general, I love female bodies much more than males. And in the males I do like, they generally have feminine features to them. They just seem to flow better. Not as choppy or roughly put together. Obviously, I don't like overly muscled guys for that very reason.
But most favorite in men...I like strong jaw lines. Nothing more lovely than a man with a very defined face, and a nice sharp, clean jaw line really brings out the eyes in my opinion. Even if they aren't particularly expressive eyes, it just gives a more subtle, sculpted look to the entire face, neck, and upper chest/shoulders. Weak or understated jaw lines leaves the upper body lacking, I think. Like it all just sorta melts together, even in fit men.
Women... probably the most understated curves on the body. Neck and collarbone, spine/curve of the lower back, feminine hands, catty eyes. That sort of thing. Again, the defined jaw.
Least favorite...hm. Not a huge fan of lower legs/calves. Or feet. On either gender, but particularly men. Arms can be a little weird.