MGM controller do I go for amperage or cell count??

[BrianG]

For reliability and warrenty (should you need it) reasons, I would select the model that matches the voltage you plan to use. The 16018 might be able to handle 8s A123's, but would be pushing it.

As far as the current rating is concerned, I would think the 16024 would be the way to go. At 8s A123 and 160A, that's over 4,000w (~5.6Hp)! Besides, I think the A123 cells will be the limiting factor current-wise.