I have both as well, I use both, generally the Chromatron has clean duty and the XD I mix fuzz pre and post pedal. From the start though my opinion has been the Chromatron is way easier to dial in, the expression input is much easier as well, the way the loop incorporates other pedals is pretty much seamless, like you're combining two or more pieces of gear, the XD is simply not. XD is very fun, I wouldn't have it if it weren't, but it can be tricky depending on input and what pedal is before it. I've also had less noise issues with the Chromatron, even with as much as 10 pedals in its fxloop, possibly a analog verse digital thing?
The Chromatron is simply surgical but musical at the same time, just like the octabvre, it just works, every time. I think a four pole option would be interesting, but not comparable to the XD, when I back off the 4>2 pole on the XD, it still reacts nothing like the Chromatron.