7* Choices for GB:
* Edea (as has been noted) is the top choice for cost vs benefit. A single Edea is enough to give an optimal 6* team an edge over similar optimal 6* teams.
* Alias - personal favorite, but he is worth it. Amazing damage (211k) and can be protected by your optimal front line of tanks and whatnot. He's note as fragile as a Glass Cannon, but he's not a tank either. Very good cost vs benefits choice.
* Ethelred7 - she's been rising in price as of late because she's arguably less bad thanks to other bad 7*'s. If you can protect her, she hits like a bus, but she's slow.
* Lierna - Glass cannon, needs protection, not a tank. Hits fairly hard but you have to make sure she's not 1st, 2nd, or 3rd in the list - she can't take much damage.
* Christina - decent damage. Again, not a tank, but when she hits, she does leave a large dent in 6* teams. Less effective against sub-optimal 7* teams.
* Cella - cheap. Last resort. Deals damage just above what the best 6*'s can offer. Not a tank.