Roster Help - Next 6* Rank Up

Ender5120

I have a 1-2 6* Rank up gem. I am also about 2 catalyst away from the ability to do another rank up. Should I keep waiting for a better champ pull to use it, or save for a R3 rank up and do al at the same time? Either way who should I rank up next?

Bulmkt

In my opinion R2 Hulkbuster

Outsider is Abom OG if you also own Red Guardian - the stacking poison damage is pretty good