I would recommend Zhang because she is decidedly more threatening than Malia, GHEIST has such high damage that +3 life is not going to make a big difference, while +4 damage will help you get them out quick. I should know, you will see me out there playing mono GHEIST this week.
Cards that hold up against SoA:
After that, you're in trouble using Sentinels. No matter who the 7th man is, you'll have some sort of SoA difficulties. Sentinels really struggle against SoA, as SoA cripples their damage or power scores.
The upside is that Sentinel actually hold up well against SoB.