I too, have two systems, but I'm keeping both. I have a 3 gallon that feeds 2.5 gal kegs, and a 10 gallon system that feeds 5 gal kegs.
The main criteria that dictate my brewing activity are time, or lack thereof, and weather, i.e. it gets really cold here in the winter.
During the winter, I have lots of time to brew, so I brew in the kitchen with the 3 gal where it's warm and cozy.
During the other months of the year I have very little time to brew because of my work, so I brew on the big system to produce 5 or 10 gallons of kegged beer because I know it may be quite a while before I can brew again.
I have to say that I love brewing on the 3 gal rig. It's just so easy, and simple, like it used to be before this hobby got so hopelessly out of control. 🍺