Well, given that most people on this bike forum state a small (16") bike is good for someone below 5'7" and a large (20") bike is for 5'9"+, I took the middle road and asked him to order me in the medium (18"; I am 5'8"). I am not worried about the medium being a little too big, but I am worried about the extremities of the size difference the small or large might have with me.

I also ended up going for the Dark Blue/Blue version as he was able to get it in earlier now (hopefully by tomorrow or Monday). I am surprised that nobody on this info-packed site has any information between the Unity Groove Plus and Giant DJ saddles.

Also, I like the Dark Blue/Blue version because it comes with the MTB Trail tires which appear (in photos, anyway) to have a little more grip than the partial slick DJ/Urban tires (Kenda K-Rad) on the Gray/Black version.