Unfortunately for us fans, we don't really have any insight at all into the most important qualifications for the job - and that is really how good they are as a basketball coach. Any of these guys could be basketball wunderkinds as coaches, and we'd really have no idea. So, as a fan, the only criteria that we can observe are:
1) Well established NBA player (which is an assumption that the players would respect them - which is, of course, an assumption)
2) Coaching pedigree (number of years as an assistant under coaches who are regarded as good)
In my view, Billups has the best metrics for #1, but the worst metrics for #2. When you factor in the sexual assault history, he'd be my least favorite choice (again, we have absolutely no knowledge of his coaching skill).
Sam Casell would be second best for #1, and has a good pedigree for #2. So, based on the extremely limited information I have, he'd be my first choice.
Udoka and Ham have great pedigrees, but don't have the same NBA cred as Billups and Casell. Of course, they could be much better candidates and be better at relating to the players, despite the lack of the NBA player experience. No idea.