There should definitely be a ~two-comic buffer before any bet gains validity... otherwise, the best strategy by far is to not bet until someone's in deep, and then bet on that character. The "death process" of a character is, statistically, pretty likely to begin at least one strip ahead, if not even more.

Sure, a character can go from totally un-threatened to dead in a single strip, but that's not the norm.

Therefore, I'm betting on Belkar.