Unless working on an existing project or platform, I tend to lean towards a documented set of conventions, such as Zend's: https://framework.zend.com/manual/1.12/en/coding-standard.naming-conventions.html
Plus this means you can use tools like PHP Code Sniffer to ensure everyone sticks to the convention.
Either way, Consistency is the name of the game. It makes it a lot easier for others (including yourself months from now) to get up to speed on a code base.
