I only do 10 gallon batches that are "house beers"- that is something I'm going to want to drink 10 gallons of! It depends on how many taps you have, or how much bottle storage, of course. I have three taps, and sometimes I'm glad when a 5 gallon batch is gone!
I make 5 gallon batches of beers I like but don't love- oatmeal stout, Belgian, porter, etc. But I make 10 gallon batches of beer I drink more than 3 pints a day of- IPA, APA, American amber.
I try to keep three different beer styles on hand all the time. That way, I can have an oatmeal stout after dinner, but an APA and then an IPA later on!