I would say Slender, but strong. I like to see muscle and just that they are strong and have firm skin covering them. Not beastly like a huge cross country runner or something, but strong enough to not look scrawny.
im not a guy obviously lol but my mom told me that my dad fell in love with my moms legs. my mom and I have curvey plump,not fat, legs. I don't know about any other guys but all the ones I know are always looking at my legs haha anyway I hope this helps.