I've rarely read posts in this forum talking about cities giving extra coin and buy (I guess it is assumed to be a pretty rare occurrence?), only about cities working as a super-lab, and the most common level associated with city in this forum is 2 : "level 2 city". So I'd say that the unspoken consensus is 1/2/3.
Logically, it should be 0/1/2, since that matches the number of empty piles, but for people with RPG culture but no programming culture, level 0 sounds awkward... My two cents.
I voted 1/2/3, because I believe that's what people believe around here. I'd rather refer to it as 0/1/2 though.