Neither
SD and 4D indexes are almost equally inaccurate for DD play. Before I used CVData to generate my own DD indexes, I used the average of the SD and 4D indexes in the appendix of the 1980 edition of Professional Blackjack for DD play. This isn't ideal, of course, but it's better than using either SD or 4D indexes.
If you happen to be playing 2D, H17, DAS, I uploaded the precise indexes at Gorilla Blackjack.