I am 5' 9", weigh 170 pounds with a slim to medium build. The Marcello classic shaped fit in size Medium fits me perfect. I do prefer a size Large for the tees and polos for a relaxed, slightly off the shoulder fit.
I am 6' 2", weigh 210 pounds with a medium build. I do have a medium sized belly. The Marcello classic shaped fit in size Large fits me perfect, but is not loose. I like my polo and tees to fit comfortable to loose and choose size XL.