I have no desire to try carbon because I believe it's inferior to steel it terms of toughness and durability. And I also have an old aluminum MTB with a rigid steel fork which is holding up great after many years of hard riding. The only issue with aluminum frame is a bit of galvanic corrosion on the lower chainstay bridge and that is the result of road salt corroding a steel bolt and reacting with aluminum. My steel frames had rustroofing oil sprayed inside tubes and there is no rust even after many years of winter riding.