One-steps aren't very common but if you're a candidate for one I'd definitely say go for it. But also be aware that no surgeon can guarantee a one-step. The assessment about whether to proceed with it happens once they've opened you up. You probably should run from any doctor who absolutely guarantees that s/he can do your surgery in one step.
The advantage to a one-step (other than no ileostomy) is that adhesion formation may be lessened. One of the places some adhesions form is at the stoma site so this would be eliminated. It doesn't mean that you definitely won't have adhesions but at least you wouldn't have them there. (And many people don't form adhesions so it's not something to be overly concerned about.)
I also think that the fewer times one is under anesthesia the better. Every hospital stay has risks and the fewer hospital stays the fewer the risks.
And I'm just a big chicken about surgery and hospitals so I would personally do anything to avoid them. I had a 3-step because I was so sick. So you'll want to have surgery being a healthy as possible. I've actually never heard of a surgeon performing a 1-step in an emergency situation (unless Thomas, Connie's son fits that bill).
Good luck with the decision-making process and welcome to the site.