I think you're asking one of two things. Actual service (who actually GETS the subpoena) should be made on statutory agent of the LLC. Each business entity is registered with the Arizona Secretary of State, and the AZ Corporation Commission has a searchable database that lists the statutory agents of each company. You will need to hire a process server to deliver the documents to that agent.
If your question is which of those two individuals you should depose, you can let them identify the most knowledgeable individual. Rule 30(b)(6) of the Arizona Rules of Civil Procedure lets you identify a specific topic to be discussed in a deposition. The recipient of a subpoena for a Rule 30(b)(6) deposition is then obligated to identify the best individual to discuss the subject matter.
Depositions are actual court proceedings with their own set of rules. You should have an experienced litigation attorney representing you so that the testimony you solicit in the deposition can be admitted later on at trial.