They're pretty different watches. The SD doesn't have the classic cyclops...and the Sub is the new one so has the cyclops and the ceramic bezel and the fat CG's.
Personally, I like the SSD. It has it's inaccuracies (font on the bezel is a bit off, usual rep pearl sucks generally) but the weight of the SD compared with the gen is more to my liking. Subs (even the new ones) feel a bit light for me for the most part. If I want light, I'll go with a DJ for the most part.
If you like the ceramic bezel, look for the GMT II...nice!!