Ranked Choice Voting (RCV) is a superset of many different election systems, with Single Transferable Vote (STV) being one of them. So every STV election is a RCV election, but not every RCV election is an STV election.
RCV defines how the polling works: There is a list of options and each voter is asked to rank them from best to worst (or refuse a ranking for those options they don't want at all). But it does not say how those rankings provided by the voters get interpreted.
STV is one method for how ranked choice results can be interpreted. Another example could be Instant Runoff Voting. Depending on which method you use, you might end up with different results for the same votes. There are more ways how a ranked choice ballot could be interpreted, but these are the two most popular ones. If you want to know more about the differences between these two systems, check out the questions How does Single Transferable Vote work? and How do instant runoffs work?.
Which RCV counting system is "the best" is a matter of debate. It depends on multiple factors, like if you are looking for the choice which makes the most people happy, or a compromise which makes the least people angry. Or how much you care about eliminating effects from tactical voting.