Which design is most preferable: test-create, try-create, create-catch?

So, do we have a clear winner or it's more a matter of taste?

The first option has a fundamental flaw - it's never going to be thread safe or safe if CreateUser relies on external resources, and other implementations may create in between your tests. In general, I tend to avoid this "pattern" because of this.

As for the other two options - it really comes down to whether the failure is expected to happen. If CreateUser would be expected to fail on a somewhat normal basis, the Try* pattern is my preference, as using exceptions essentially becomes using exceptions for control flow.

If the failure would truly be an exceptional case, then exceptions would be more understandable.

Test-Create can cause race conditions, so it's not a great idea. It also likely does extra work.

Try-Create is good if you expect errors to be part of normal code flow (such as in the case of user input).

Create-Catch is good if errors are truly exceptional (so you're not worried about performance).