I've used their D2 on a mini-Grip and S30V on a Ritter mini-Grip. They both seemed about the same to me (took a great edge and held them about the same). I didn't do any controlled testing or anything. Just my observations after EDC'ing them for a while. Both hold a sharper edge longer than the standard 154CM from my experience on a mini-Barrage, mini-Grip, and large Grip. Again, no specific controlled testing, so I can't say which cut more/less of what materials in between re-sharpenings.
I typically don't sharpen my D2 to anything finer than 600 grit though (vs. S30V and 154CM, which I will take to 1200 or 4000 grit). For some reason, when I go higher than 600 on the D2, it starts to lose some of its bite. I'll fault that to my sharpening skills (not the steel itself), but even at 600, it will easily push-cut newspaper as well as the blades in other steels (my typical test for when it's "sharp enough").