I think this is one of those subjects that will always be hotly debated -- i.e. whether a 1 step vs. 2 step vs. 3 step is better. And I don't really believe there is a right or wrong answer; rather, it depends on your own individual circumstances.
Currently, I believe that the 2 step is still the most common for j-pouch creation. Many feel, as does my own surgeon, that a 2 step is more ideal than a 1 step, since diverting with a temporary loop ostomy and allowing the pouch time to heal amounts to greater success down the road. The bonus with the 1 step, however, is that you avoid the loop altogether, and potentially reduce healing time and scarring because it's just one surgery rather than 2 or 3. I myself ended up having 3 step surgery, but that was because I needed emergency surgery to remove my colon and at the time I didn't have the luxury of waiting to see a colorectal surgeon skilled in j-pouch construction. It was basically "get the colon out now so you don't die, and then we'll re-evaluate options later." Which is what I did, though I ended up living with an ileostomy for over 2 1/2 years.
As Jan said, though, it depends on your situation. Like me, sometimes the colon just has to come out ASAP and that usually necessitates a 2 or 3 step. There are other factors as well, including whether or not you were taking steroids, your overall health at the time of surgery, your surgeon's recommendations and/or general preferences, your own wishes, etc. It's always best to discuss these things with your surgeon and determine together what is right for you in your particular situation.