Which rank up should I do next

Angelfire_TNOR

I'm mostly working on Variant 2 and 3 and Act 6.

I already have a 5* Stark Spidey and Domino at Rank 5.
All Ghost synergies can be completed with 4*s only
Have a 4* Ghost Rider for the 'Holy Trinity'
Have a 5* Champion (un-awakened) for Thing cheese