Between the First and the City, I'd pick City as a first bag, simply for its bigger capacity.
If you like how the First looks, but want more capacity plus the advantage of a cross-body strap, then how about the Town? I bought one, initially thinking it would be an occasional-use bag for me. Surprisingly, considering how much I normally carry, I've found the Town fabulous! I only need to carry my sweater or leather jacket on my arm, as opposed to when I carry my City, which can fit either in.
Being the size in between the City and the First, the Town is definitely worth considering and trying out if you don't carry too much around (or are a clever packer) and would like a cross-body carrying option.