I have been auditioning for a couple of years now and I say if you can have more... then you should. For example, I have two monologues that I am ready and comfortable to go any moment which are from Smart People by Lydia R. Diamond (within ten years) and Uncle Vanya by Anton Chekhov. I love having more monologues now because the auditions I see either ask for contemporary monologues or before Tennessee Williams. If you are auditioning for a season- you need contrasting monologues. Sometimes they only need one! Look at Playbill or Backstage for a better insight of how they want their actors to prepare. Callbacks are sides.

It also really depends on what you want as an actor. Do you want to do Chekhov? Do you want to be a Shakespeare productions? Or you just a contemporary gal? The plays I love- I see those auditions ALL the time, and I regretted not being prepared with more monologues.

Also the theatre you try out for- I'm with a company that does cutting edge stuff, so I auditioned with Smart People. Read plays that are just got off Broadway or produced in well known theatre stages.