Which ones should I rank

Naayahs

Completed 50 percent of act 4
Corvus, nick, arch is rank 3/5
I heard the 5*s I have are bad

Luke9523

Focus on your 4*s for now. You have some great 4* options. Don't waste resources ranking up poor 5* Champs. You will get better 5*'s in time.
Corvus, Nick, Arch, Herc and Red Guardian should get you through content until you pull some better 5* Champs. 👍👍