Who should I awaken?

Hollowborn

I have a 4* mystic gem to use

Blitzkilla420

awaken gr (if you have to pick a mystic from that pool) awakened he can easily pass a judgment with his duped ability (ending combo on med attack) without using your bleed judgement (ending combo on light attack) or s1 judgement and therefore can stack more judgements for more regen (heavy attack) or more fate seal (s1) or more power drain (s2) or a longer s3.

gr has the best and most utility out of all those choices