xboxdrv
xboxdrv is an alternative to xpad which provides more functionality and might work better with certain controllers. It works in userspace and can be launched as system service.
Install it with the xboxdrvAUR package. Then start/enable xboxdrv.service.
If you have issues with the controller being recognized but not working in steam games or working but with incorrect mappings, it may be required to modify you configuration as such:
/etc/default/xboxdrv
[xboxdrv]
silent = true
device-name = "Xbox 360 Wireless Receiver"
mimic-xpad = true
deadzone = 4000
[xboxdrv-daemon]
dbus = disabled
Then restart xboxdrv.service.
Multiple controllers
xboxdrv supports a multitude of controllers, but they need to be set up in /etc/default/xboxdrv. For each extra controller, add an next-controller = true line. For example, when using 4 controllers, add it 3 times:
[xboxdrv]
silent = true
next-controller = true
next-controller = true
next-controller = true
[xboxdrv-daemon]
dbus = disabled
Then restart xboxdrv.service.