I dont know where you ride, but I ride on very rocky trails and you really cant beat the protection you get from steel.
The plastic rip too easily and the aluminum are good, but they tend to grab the rocks and not slide over them.
The best and easiest thing we did, if you have access to it, it got steel about 1/4 thick and cut our own guards and then welded them in place. Very strong, cheap and effective.
Jim