We have a little rota of cities (Krakow, Prague, Bruges, Amsterdam, Tallinn) where we return to for short breaks, maybe once a year, as if we are there for only 2 0r 3 nights, say, it is nice to have some familiarity with where we are and to our return to favourite places - especially restaurants and pubs/bars!- as well as discovering new ones.
However for longer holidays we tend to look for places that are new to us in order to experience and explore different countries and cultures etc.. So ideally, finances and time permitting, it would be one new and one old per year!