Good review.
I guess it comes down to whether you are playing the long or short-term game.
If you want the short term saving, model for model, the Citigo looks like the best value. If you are playing the longer game - when either overall cost of ownership is more important or if you are keeping the car for many years, then I believe the up! is the best option. What's £500 over 5 years when you get a better looking (IMHO), better finished (just look at the dash, seats, boot floor) and lower depreciating car.
The Mii is somewhere in the middle.
I deliberated long and hard between the up!, Citigo and Mii and have no doubts I made the right decision.
Incidentally, despite their general reputation, even Skoda dealers aren't perfect - I am still waiting for the call from a local dealer to tell me their demonstrator has arrived. I gave up waiting mid-May and went to another one to try theirs.