My suggestion from experience as I let mine expired for a few years. You must do one plus an extra. Here is how it goes, if you do your CFI, you'll have to do the MEI also. Same with CFII. My DE had a ton of experience and he suggested doing the MEI, with the CFII (doing some approaches/instrument). That way you don't have to rent a S/E and a M/E airplane and paying twice. The oral was based on both. Saves you lots of money, so ask your local DE if that would work for him/her.