I love whatever format system I happen to be shooting on a particular day. It helps the creative juices to switch things up from time to time.
But once I'm in the darkroom things are no longer equal. The bigger the better, meaning 8x10 is my favorite film size, then right down the line.
Medium format is awfully nice when it's just too windy or rainy for a view camera (and when I want a larger neg than 35mm), for quick pot shots from the highway, and for vacation travel (when my wife gets impatient if I set up a view camera). I also sometimes take "finanacial
vacations" from the cost of sheet film by shooting 120 roll film.