Irene, check out this thread as well and see my post#51, showing both sizes side-by-side : http://forum.purseblog.com/balenciaga/first-or-city-35246-4.html
Would vert gazon color be as hard to locate as apple green?
The First works great for me if I don't need sunglasses... but my enormous Prada sunglasses case takes up a lot of room. My mum makes a First work with a water bottle, wallet, keys, phone, iPod and an extra little pouch for cosmetics and things.
If you carry more stuff than that, I would say go with the City. There's a reason it's the most popular style!