If you're only comparing the figures off-the-shelf, then I'd have to go with the original deluxe Sideswipe. At first I thought SA SS was better, however they both have a lot of back kibble, SA SS has a tiny head, and neither stand very well. I like the original just a bit better because he is screen accurate (which is very important to me) and looks better proportioned.
HOWEVER, if you're willing to do a little extra work, DOTM Sideswipe can be almost as good as the original. I did a simple paint job with mine-I painted all the light grey parts silver-and I think he looks awesome. He still has the inaccurate chest, but his feet are much more stable, I like the swords a lot more than the original's, and he's nicely proportioned. Plus, I think the backpack is slightly less obtrusive than the original's. Plus, with the paint on, he holds together much better in alt mode.
I'll post pictures once I get home.