There are plenty of interesting reasons why Dr X or Professor Y might be good examiners:
- They’re experts in your general area;
- You’ve cited them a lot;
- You’re hoping to build your network a little.
You don’t get to choose directly. Most candidates can at least have a conversation with their supervisors about who they think would be a good choice. Think through what you might look for, and see how that conversation goes.
There are also interesting reasons why Dr X or Professor Y might not be acceptable as examiners:
- Maybe you’ve had lots of conversations with them about your PhD work;
- Maybe you’ve had correspondence about working with them on a future project;
- Maybe they’re part of a collaboration with your supervisor.
Depending on the rules of your institution, these possible conflicts of interest might disqualify them from even being considered. If you’re concerned at all then it is worth checking.
The first list comes down to preference: the kind of examiners you want depends greatly on what qualities you see as being valuable.
The second list comes down to policy: some people won’t be acceptable because of how you’re connected to them.
You should definitely think about the first list in advance of your viva; in some cases the second list will be just as valuable to narrow down options.