It's difficult to tell - we are not likely to have a new Tory leader until late autumn at the earliest. Offhand, of the older generation, David Davis appears to be the best organised - sound politically, but not exactly inspiring. An offbeat choice would be Theresa May. There is talk of the new shadow chancellor, George Osbourne becoming the leader, but I think he's not well known enough...yet.
The hope I have at the back of my mind is that Greg Hands can get well known in the interim and becomes a contender in what is a very short time.
Regards, Ivan