I literally scremed "Yes, GO-TO!" when I saw this!
I said the same thing when I saw GO-TO!!
O.K., I have to give this one to GO-To as well. With that fact that he is a droid(meaning no force sensing) and all the other points you listed, GO-TO will win.
I know little about Plagueis, but some of his force powers seem to make him extremely hard to kill. Luckily for GO-TO, I think he may die yet.
Plagueis is somehow able to find GO-TO's ship, and gets safely through. The sun guard (from what I read on wookiepedia) would not be with him, as they served as guards on the moon Sojourn. Unless Plagueis specifically asked for the guards to come with him, they would not.
Anyway, Plagueis is inside of GO-TO's ship, and believes he has captured GO-TO. All GO-TO needs is for multiple assassin's to attacked Plagueis at the same time with some type of paralyzing poison. Plagueis' Heart Stun wouldn't be able to overcome that, and even if he managed to kill the assassin's afterward, GO-TO could've escaped, or gotten in for the kill.
Please correct me if my information is wrong, but I vote for GO-TO!!!!
EDIT: Dang it Aurbere, you beat to to the post!