Lou from Farmington Hills is about to ruin the last "Sopranos" for you: "I just had an epiphany about the ending of the 'Sopranos.' It fits into one of your three possibilities, but it could almost be its own category: Tony gets killed by Janice. We know that Bobby was talking about DNA, and the kid he killed ripped his shirt. He's probably got fibers under his fingernails and those fibers have sweat and whatever on them. Anyway, that's going to get Bobby arrested, and it's going to piss Janice off. She knows that Tony ordered it, so she'll blame him and end up killing him. She's done it before. I think it fits in perfectly because when you think about it, the women have been the most powerful people throughout the whole series. They pretty much control the men and their happiness. Also, in closing, Janice is effing crazy."
(Agree with everything. Also, it would make sense if David Chase's original plan for the last show was to have Tony's mother kill him -- a premise that's seems plausible in the pilot -- but since she died in real life, Janice took the torch as the female Soprano who kills Tony. Also, we've already seen her blow away Richie Aprile, so we know she has it in her. I like this theory.)