The different angles on the bangers are there to keep the bottom of your bucket parallel with the table so you don’t have to hold your rig at a weird angle (which can make your percolator not function properly). A 90° banger is going to be the most popular, as most female rigs have a fixed down stem. The 45° angled bangers are typically for beakers or rigs with a removable down stem that also sits at a 45° angle, which will keep your banger in the perfect position.
This is our favorite Elev8 banger
https://www.elev8glassgallery.com/elev8-glass-quartz-flat-top-thick-walled-banger/