Woz? From everything I've ever read by or about him, he's got absolutely no interest in running a corporation. If they forced him into it, it would be interesting, but the company would bleed red ink before it died. He'd come up with great ideas for products, but I don't think he has the slave driver capability to get them out the door. (And bless him for that and for being who he is.)
Phil Schiller would be a great interim choice in the event that something happened to Jobs, like, tomorrow (e.g., the ol' hit-by-a-bus scenario). He could steward the company through a rough time, but I don't know if he's got a long-term vision to keep it moving forward. He would, however, be crucial in picking a permanent replacement; he "gets" Apple.
The thing about Jobs' tenures as CEO is that while the man returned, the manager in the second era is very, very different. And much of that would seem to be due to the drama of creating a company from scratch and having it all taken away. He runs things based not only on a determination not to make the same mistakes that he made the first time around, but also to not make the mistakes that the people who followed him made, either. That's some hard-earned wisdom that not a lot of corporate executives have.
It also means that whoever takes over is going to have a thankless time of it. Apple is never going to be his or her company. There will never be any creation myth about him or her building the first machine in a garage with a buddy. "[CEO-elect's name here] bought his first Mac with the help of his father's credit card when he was sixteen years old" just doesn't have the same ring to it.
So, in short, I have absolutely no ide who would make a good replacement. If Apple is smart, there's an ever-changing short list of people to approach if something happens, always evolving -- names added, names scratched off -- based upon what Apple's needs are and how well those people could serve them.