Your theory about Sheva is strange. I play with Sheva (not with the default: Chris) in re5. If we follow your theory, my Chris is the annoying character while i'm playing on professional ^^.
Best characters: Cindy and Alyssa Ashcroft. Why? First: because they are girls (to me that's enough to be one of the best ) and; second: they were just normal people. Not heroes with any kind of survival training (no basic police training with guns as Leon, no special team training (S.T.A.R.S.) as Jill and Chris. They are a normal waitress and a normal reporter. Hope they release outbreak file #1 and #2 for ps3 or even bring a new outbreak (#3) for this console.
And last, but not least: Jill Valentine because of her story. Only woman on S.T.A.R.S. alpha team, kicked nemesis **bleep** (a wonderful adversary) and suffered a lot as a guinea pig in the hands of Wesker when she was captured by him. With all these things she went through, she still survives (and it's a GIRL, not the usual muscle man. She's AWESOME). The best example of survivor i've ever seen on video-games. EVER! And now her body is immune to T-Virus. The scientists can create a good antidote for T-Virus from her cells and; if this virus "leaks" again (It looks like it'll appear again in re6) , it'd come in handy for normal people. ^^