My choice would be [spoiler]Vicki's. We learned in the Leviathan story she got killed by Jeb[/spoiler] but to me that was just a stupid and unnecessary plot twist to throw in there. I still refuse to believe it.
I also would have [spoiler]let Beth live, with or without Quentin. She seemed doomed to die even with history changed, which I think is sad because I really liked her and believed she really did love Quentin with all her heart and soul.[/spoiler]