I have to go with Abraham. Negan rules by fear and Abraham, in true Abraham fashion, didn't show any, as someone else mentioned. That would be the smart choice for Negan and I believe he's pretty smart.

I think the episode was great because it exposed Rick to the reality that they can't handle everything. In hindsight, he should have gotten even more cocky, listened to Carl, and engaged the first group they ran in to. It was out of character for Rick not to do that, he had fairly equal numbers and, based on how easy it has been to kill Saviours, everything would be pointing to an easy task in dispatching that small of group.