The SD is 7 pounds lighter, and had the upgraded seat and padded side rails. Better is relative, I liked the seat height with classic better than the SD, the comfort seat sat lower for me than the classic, an issue standing and drawing over the rail.
Same size platform and climbing design.
For bowhunting, the classic did all I needed, but it is a "heavy" stand if you are hauling it in and out of the woods.
The Summit shoulder straps are marginal, you'll probably want to get padded straps for it.
I still have my classic, and probably will for a while, as a backup for my Lone Wolf.