Hmm I like the Moscow metro for some reason. The only thing with it is that you need to figure out the cyrillic letters, but that isn't too hard. You also have to pay attention when changing lines. I got to the exit once and I broke the rules and jumped over the fence to get to the escalator down again. And it's cheap too. 25 rubles no matter how far you go and as long as you stay inside the system, transfer to other lines is free.