For me it was the clearance. I ride smaller bikes (50cm Kilo) and the clearance was just too tight. I had a 48t chainring with a 16t cog, and with a 25mm tire, it left about half a centimeter from the seat tube. Keep in mind this is probably because I was riding a smaller frame. The steamroller fits my 32mm cross tires no problem, and I even have some clip-on fenders that just barely fit. I had to buy a different brake though, but the FFF chainstays made the deal. I was sort of hell-bent on getting a more aggressive track geometry, but I found that the Steamroller is a perfect balance of tightness and comfort.
As far as completes go, the components on the Surly are a bit better. I've heard god-awful things about the Kilo's wheelset. The wheels on the surly are much better, and Surly themselves make a pretty decent hub. Only thing I'd change on the steamroller is the seat.