I try to create a balance between what I think I want to drink in the next month or two, whilst also thinking about trying to have at least one, possibly two, beers that people who come to visit might really enjoy. In recent times I've discovered the joys of bone-dry german-style cider, so that's been taking up one of my 4 taps. The other 3 are usually made up of a malty or reasonably approachable beer, a hoppy beer and a big beer. Things have gotten towards the hefty side this winter with a big oatmeal stout, ipa and tripel making up my tap list. Will be following that with some more sessionable styles.
I don't ever want to have more than 4 beers on tap, as I don't think I'll get through them quickly enough. I like the idea of enjoying my beer on tap super fresh.