Who should I rank up?

Reisthetic

I just got cavalier,im swapping to 6 star ranking now, hope to get some help on who to rank up.

Qacob

Stealthy, mags, spam and Ultron are your best bets imo.

Magrailothos

Magneto and Ultron are both fantastic champions, who'll be useful for years. Neither really needs their Awakened ability, although they're nice to have.
Stealthy is really good too - a bit slept on, now.