I just go grab whatever razor I feel like. Some days I feel like using a wedge or quarter hollow, other days I want to use a full hollow or a frameback.
Sometimes I use one razor all week and occasionally I'll have a Sheffield or Eskiltuna week, those are the only times that my choice is premeditated and even then I have at least some variation.
having a set rotation would take away some of the fun for me since I pick soap/cream A.s and razor based on my mood that particular morning.
"Informal rotation" is definitly the way to go if you ask me.