I've been reading an a lot of guys are saying go with ATF so I may do the same.I run atf in my primery because I have revira pro clutch. an ATF is supper cheep.
Your owners manual and factory service manual probably tell you H-D fork oil type E. Be aware that fork oils vary greatly across the brands, so there is a risk that the same grade will behave differently when swapping between them. As for ATF, that is neither a suspension nor primary oil!