I own and carry both and they're pretty similar as far as useability, reliability, and smoothness. They're close enough that I wouldn't let the difference between them be the deciding factor between two knives.
SOG really has a winner with the Arc lock, and if they made a line of Arc lock knives that were otherwise comparable to Benchmade/Spyderco/Emerson* we'd see a lot more people here buying, carrying, and talking about them. I really don't know why they haven't done all they can with it, but I know they have sold less knives because they haven't.
* When I say otherwise comparable to Benchmade/Spyderco/Emerson, what I mean is a handful of different models with 3"-4" blades, full double liners, 154CM steel or better, G-10 scales on most, different blade and handle shapes (interchangeable would be good), MSRP between $100 & $200, a few different sizes, choice between plain and combo edge, etc. AFAIK, the only knives SOG has done this with was the Vision series, which didn't do as well as they could have because tanto was the only blade shape offered, and they only came in combo edge (except for a small sprint run at MSRP only). If they had made some other similar models with the features we've come to expect, I think they would sell well.