Looking at a few on YW, I noticed that there's about a $10K difference in asking price for the S2 vs the Sabre - for similar apparent condition. Assuming that's your situation too, and it's manageable then I'd go for the S2 (condition and equipment otherwise equal)
I like the layout better, of course the extra length gives you more space but more to the point is the fact that you do not step on the galley counter as you enter the companionway. Also the offset U-dinette is nice to have in that access to the forward part of the boat is not necessarily always blocked with more than two at the table. The S2s galley is also a better work place for the galley slave, and should be more secure in a bit of motion.
The cockpits seem comparable, though again the S2 appears slightly roomier.
Sabres have always had a good name, and that's a nice looking classic boat with a traditional layout, but if you can swing the diff then I think the S2 would be more liveable, and likely a slightly better performer.
btw, you didn't mention if the S2 is the "A" or the "C" (center cockpit) model - my comments are based on the aft cockpit version. I'd expect with the center cockpit version you'd gain an illusion of privacy with some cost to spaciousness below.
Disclaimer: I've not sailed either of these boats, so keep that in mind too