I've given up guessing, I never get it right anyway. I do like that anyone can die at any moment though. The Red Wedding was immensely satisfying for instance, but after that and the death of Joffrey, there's really no one else I really want to see dead.
As for who dies next... There are many obvious match-ups which could take place in the "Trial by combat", but R.R Martin never goes for the obvious, and I guess there will be some sort of insane twist in the Tyrions "Trial by combat", and that even trying to guess who's going to be the champions is a pointless exercise. So yeah, I'm going to be boring and not even make a guess. The only thing I absolutely know for sure is that I'd get it wrong if I tried.