It's up to you. Would you prefer to have gears clashing due to heavy lube or smooth shifting gears that may wear faster due to ATF. Either way they're takin' a beating. I have tried pretty much everything available and for me ATF is by far the best. Fair amount of brass "glitter" on fluid changes, but not much that will stick to a magnet. Ya'll gotta stop thinking about these things as daily drivers and realize that even with potential accelerated wear rates they'll probably outlast your grandkids..