I'm probably in the minority, but I look at the CB last on a good majority of my shots. I've tried several times over the years to focus purely on the OB, but I just can't. Don't know why, just the way I learned, I guess I used a lot of english naturally (also a bad habit, breaking that one now) and figured if I aimed correctly while standing and got down correctly, that once my eyes locked in the aim line then it was more important that I hit the cue ball where I was aiming and the rest would take care of itself.
I know that goes against popular instruction and maybe even common sense, you know the rifle analogy and all of that, but at this point after 20 years I think it will be tough to change. I feel like I lose control of the shot if I don't stare at the point I'm about to hit. But there are times when I do focus last on the OB, and in practice it turns out just fine. A matter of fact, sometimes it helps prevent any occasional flinching or steering action, since I am just focused on following through to my target on the OB. One of these days I'll be more committed to doing it more and more in practice until it's comfortable enough in pressure situations, but I can play lights out the way I do so low motivation at this point...
As for the break, I look at the CB last - I know, big surprise, right? On that I'm more divided, I know some people advocate still looking at the OB last, but even if I get to looking at the OB last more on normal shots I still think on certain specialty shots like jumps, jacked up draw shots, masses, and the break I would feel better looking at the CB last.
Scott