Already have a duped r3 6* N.Fury so should I also r5 my 5*NF or a diff skill champ* for other uses:

Tainto

*All awakened

Berlad8

If you have 6* champs at r3, i don't think you should continue to rank up your 5* roster unless you have a lot of expiring resources without any use.
but if you don't have a lot of 6* and you need to rank up champs to progress, i'd go with Stealthy or Monkey.
otherwise save your resources and invest in your 6* roster.

willrun4adonut

Monkey

Though I'd r5 your NF. But I didn't see that option. I use both of mine frequently (one for war defense and offense/questing).

Lovejoy72

I like having both nicks (one 6R4, one 5R5) since the synergies function based on whether he is alive or dead.

Tainto

Dang yeah forgot to put Nick as the last option. I have other 6* but honestly none I haven’t already ranked up that are as good as those skill champs I listed