Hi -
Here in this case, it comes to readability.
All have, Birmingham and restaurants are the 2nd and 3rd level subfolder, so they have the same impact.
In my view, it should be as simple as site.com/restaurants/birmingham, where the restaurants your main identifier of the keyword is closer to TLD.
Zomato.com does it very good, you can checkout that as well to inspire yourself.
Also booking.com is to some extent good.
If have to choose between the 3, i'd go with the first one
K