...which I find more readable. It's up to you whether you use the User class at all, you don't need to, though you do get the benefit of not having to call global $user everywhere you want to query the phpBB user information.
The main reason I implemented the User class in my code was to integrate phpBB with my application. I have User tables in both my phpBB database and my application database, which have a 1-1 relationship, but in my application database I store settings that are local to the application not phpBB. Centralising code for all user manipulation and interaction was my motivation for creating the User class.