Arcade Games rank up gem? Which is best coice?

Debating which 6* to use the Arcade 3->4 rank up gem on. Looking for the most useful champ overall.Thanks for any input.

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Highest utility out all of these and 7* unavailability makes her more desirable.

Depending on the rest of your roster but Valk or knull would be my choices.

Both prefer awakening and high/max sig, though.