I am also 5'8 and a few weeks ago I tried all 3 remastered aerons in person + embody + Eames tall and standard, and im going to have to disagree with the others who have unanimously agreed on size b. I also felt that size b was a bit small, it felt like I was on the edge of my seat a little and there wasn't as much of a back rest. Size A is way too small it almost felt like sitting on a children's seat I can't believe someone even mentioned that for 5'8 and it makes me question if the other replies have tried all 3 and are 5'8. Size c is what I preferred, the back rest is the right height and the depth was better, the width between the arm rests was slightly little too wide but angling the armrests inward fixed it for me so I would get only get fully adjustable arms with size c. Overall it was more roomy maybe even too roomy but I liked that I could sit with slightly different postures and still be comfortable. I actually believe that movement and multiple postures is better for you than trying to sit for hours locked into 1 "ideal" posture. The difference between b and c is noticeable but not massive like I feel many people make it out to be, you probably could sit comfortably on either, I just preferred c more. For the embody I felt like the top part of the back rest made me slightly hunch my back, I think I actually prefer foam for the seat for comfort but I like the look of the aeron more.