I'll make this quick and simple.  Let's say you have a business located in several cities.  You've built individual pages for each city (linked to from a master list of your locations).

For SEO purposes is it better to have the URL be a subfolder, or a parameter off of the home page URL:

https://www.mysite.com/dallas  which is essentially https://www.mysite.com/dallas/index.php

or

http://www.mysite.com/?city=dallas  which is essentially https://www.mysite.com/index.php?city=dallas