It really doesn't matter which you buy first because you'll buy the other in short order! That's just how bbag purchases work! My City and Twiggy were purchased just days apart, and I'll bet that's not an uncommon experience on this forum.
City For me the twiggy looks too long. I know many ladies here say that the twiggy can fit just as much as the city but to me it always looks smaller. Perhaps its the long shape? But one thing I definitely like about the city is that I can fit a hardcover or paperback book in it easily.