Functional Difference? Nope.
I have two digital and one analog, and I love the digitals much better. The temp control was a lot "tighter" on the digitals, I can set the range of when it will turn on and off within one degree. My newest digital is also a dual stage.
My analog was actually hard to "dial in' and took a bit of trial and error. Him I leave in my kegerator as temp is not that important to me as I feel there is a wider range of acceptable temps for serving. Where as fermentation I mostly leave at a specific temp (68).
I like the options on the digital, and I recently picked up an STC-1000 that was $17 unassembled. My other digital is a ranco etc 1100, which is also nice and has been my go to controller.