I prefer the look of a plumper horse, But I know it isn't as healthy. My dad is a farmer in Australia so he has dealt with drought his whole life - A skinny animal is abbhorrent to him. I constantly argue with him about how much the horses need to eat - The second I start getting them down to a healthy weight he starts feeding them back up again!
However, they aren't obese, so I don't make a huge deal out of it. At least they are out 24/7 so they are moving, I would be much more concerned if they were stalled.
I've always had easy keepers - Lord help me if I ever get a hard keeper!