Save or use 4* awakening gem

MCoC_fan

I got a 4* mutant awaking gem from the 4* awakening crystal.
My current 4* mutant champions are, Gambit, Beast, Nightcrawler, and Magneto Marvel now.
I am almost done completing act four, and a 4* crystal from it.
so with those in mind please help me with what I should do.

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Save for a later champion

Save for someone better like archangel, omega red or iceman and domino