looking to get from Munich to regensburg to prague. Upon return, would like to stay in Pilzen for a night. Bus or train bus from regensburg???
I believe trains are more frequent than buses, so planning to go that way may be easier. However, Rome2Rio's information is sometimes incomplete; there may be buses run by a more local company, not just the Eurolines and Flixbus options Rome2Rio knows about.
Check the Deutsche Bahn website for the rail schedule; it looks like there are trains about every 2 hours. Sorry not to provide a link; haven't figured out how to do that on a tablet.
Check also https://jizdnirady.idnes.cz/vlakyautobusy/spojeni/ .