Itachi, Kisame, Deidara, Konan, Jiraiya, hiruzen, zabuza, or sasori.
They were all well written deaths and are good contenders, but I'd still have to weed it down to Hiruzen, Jiraiya and konan since out of all those, they were the only one's that didn't suicide.
And, between those two, I'd go with Konan. She died to plot-shield Obito and put up a decent battle... for jiraiya, it was kinda BS that he couldn't sense Asura and the other pains in SM and got flanked so easily and hiruzen was being played the entire match, basically being fodderized.
TL;DR; I'd have to say Konan...