I think Ada is the most competent out of all RE characters, but due to her tendency to stab people in the back, I'd rather not trust her unless it's absolutely necessary. I'd say Chris, but the odds of survival in his presence are, as KennedyKiller stated, not the best. Of the male characters, I'd probably pick Jake. Without him, Sherry would have been deader than dead more often than Leon without Ada, and that is saying something!
Of the females... hm... Maybe I should go with Jill? Yes, I'll pick Jill. We've seen in RE5 that she's willing to sacrifice herself to save others when needed, and since I don't even like her, I won't feel sorry or sad when that happens.
So people never die around Leon? You have to be kidding.
*cough* Ada in RE2, in both possible scenarios (although she got better) *cough* Luis in RE4 *cough* The guy and his daughter at the university *cough* The survivors at the cathedral *cough* Deborah *cough* Pretty much everyone else who teamed up with him in Tall Oaks *cough* The people on the plane *cough* The BSAA agent who helped him and Helena escape the fog of doom *cough* And he himself quite often if it hadn't been for Ada.
If anything, Leon is the angel of death. The only difference between him and Chris is that Chris mostly loses characters who are somewhat important to him and the story, while most of Leon's people don't even have names, but it still counts. If I was a mortal civilian in a city infested with zombies and I'd see Leon coming my way (or better yet, driving my way in a car), I'd run for my life, but not in his direction.
