Not sure which driver would be best for you. However, I believe the MAG series combos had 2 speaker outputs,
so if you want to ever use an extension cab then replace the combo speaker with an 8 ohm one-that way you can add an
extension cab (also 8 ohms) to get the full power from the amp (which will then be into 4 ohms total)
If you'll never do the extension cab thing, then replace your blown speaker with a 4 ohm one - these are often a bit harder
to find though, and the difference in output from your combo with a 4 ohm speaker against an 8 ohm one may not sound that much.