Xebec obviously... it's rare a character in OP lives up to the hype and although I expected (and kind of wanted) him to be a bit more evil the hype was all still there just in a different direction. Overall, no one is touching this guy, he stole pretty much every chapter he was in.
I feel like Shanks could have if given a little more depth. Harald is just Oden 2.0, some flaccid idiot who kept making bad decisions even though he knew all the bad stuff that was happening.
Scopper had a surprisingly good intro. Based on what we saw in the flashback I wasn't expecting him to be badass enough to nail a giant. Imu has some bullshit powers but I feel like he's being set up quite well as a villain.