Question about Rotation Feeding

I have a question for those of you who rotate your cat's food. Do you guys rotate brands per meal, per day, per week, or do you finish one brand before moving to another? Which do you find better and why?  

I am both a dog and cat owner. Currently, I rotate (for both pets) by going through all of the different proteins of one brand once, and then I transition to another brand. I have found that rotation can be pretty sensitive with my dog. For instance, she can barely handle the rotation of different proteins within the same brand; for awhile, I would switch between two flavors at every meal, and it just resulted in a constant upset stomach. Furthermore, my transition to an entirely new brand has to be very slow for her not to have a reaction. Perhaps, I just have a sensitive dog because my cat seems less affected when switching brands. For those of you who switch brands at every meal or every day, do you have any digestive issues with your cat?

I am more interested in advice concerning brand rotation than rotation between wet, dry, or raw. Any advice is appreciated.

For my dogs, I just buy a different brand with every bag. Maybe once a month or so. With the cats, I mix the dry food instead of rotating. . .but only because I have a lot of cats. If I had fewer cats (and so couldn't use up several mixed bags before they went stale/rancid), I would rotate like I do for the dogs.

We rotate brands every meal, for two senior cats, and neither has ever had any digestive issues. The male was getting dry food (prescription urinary) in the morning and canned in the evening, but both are now getting wet 3x a day. The brands (4 atm) are grain-free or at most 1% rice and contain various types of meat: beef, chicken, lamb, turkey, ostrich, kangaroo, buffalo, salmon, tuna, barracuda, calamari or swordfish. The fish is mixed (at least half) with chicken and limited to two meals a week.

The rotation has been going on for over 12 years now and was at the male cat's insistence, i.e., refusal to eat otherwise.