I'm asexual, but for a guy to look okay in my eyes (as in doesn't make me turn away going "I can't look at that..") I say medium.
slim as hell looks sickly and looks like if I try to hug them they will shatter.
Muscular means veins popping up and showing and no neck...
I hate seeing veiny people with no neck... I don't even like seeing veins in general lol