That entirely depends on the type of questions...
- If you are asking about programming using rsync, use Stack Overflow (that is if you have code, a script for instance, that you can post)
- If the problem is a system administration one (say about opening ports in a firewall), Server Fault should be the place
- Super User is for general software usage questions
Each of the communities has a tour page (
<site address>/tour) and a help center with a "what's on topic" article. These give you a good idea about, well..., what's on-topic for each of the given sites.
Note that some types of questions don't belong anywhere on the network.