1: Blackbeard
The only thing to be said about Blackbeard as a Warlord is how much sense it made for someone like him to become one of them, and being a big fan of the Blackbeard storyline, I think he's got to be at the top of this list.
2: Moriah
Moriah, I think, is an outstandingly fun concept. Maybe not implemented to perfection, but done well enough to warrant praise. His 'relying too much on his crew' shtick was a breath of fresh air after the almost absurd degree of individualistic power fantasy we were exposed to earlier in the series. Honestly, I really love Moriah.
3. Kuma
I also love Kuma's design, I love him in concept as a half-cyborg, his actions are always praiseworthy, and he blends in just enough comedy to adequately undercut his serious demeanor. I've got to say though, he's still underutilized and in ways that will now never be fixed. A shocked or scared Kuma would've been all I'd need to consider him a complete character.
4. Jinbei
Jinbei has a lot that can be said about him. Personally though, his role as a follower while trying to be an effective force of good can not be understated in its simple relatable beauty and it mostly counteracts how boring his character typically is otherwise.
5. Buggy
As a warlord, he suffers, but as a design for a pirate character, I've always liked Buggy one of the most out of all of the One Piece characters.
Moreover, I've always enjoyed the near parallel journey that Buggy has gone on next to Luffy and fantasize about when or if he might be relevant again at the end of the series.
And he's comedy gold.
6. Crocodile
There are a lot of good aspects to Crocodile's character, and the Alabasta arc, where he had a starring role, was one of the best, but looking back, I kind of dislike him. There is a lot of uncertainty to his background and a lot of mystery to it. What was his conflict with Whitebeard? Whats his connection to Ivankov? But having gone this far without a reveal isn't something I really like.
At very least, I'm pretty glad that someone like Crocodile existed trying to circumnavigate the requirements to become Pirate King though.
7. Doffy
It's been noted several times that Doflamingo came off as a bit too strong during the Dressrosa arc. We had been given an impression of him as a master manipulator, and someone who controlled people like puppets, but in his actual fights, there was hardly any of that. What should've been one of the most fun parts of the arc was undercut and never really explored. I suppose somebody with his logical perspective was necessary, but I think that Crocodile did the same thing better.
8. Law
A potentially fun but highly under-utilized character. His fruit gives him so many opportunities for quacky hijinks like body switching and removing a person's vulnerable points, and his role as a parallel captain more on the logical side was ripe for interesting dynamics, so for a while I rated him highly, but he's hardly lives up to his stated potential at all. I'm still going to hold my breath for the next 20 chapters, but for now, I've honestly got to put him low for being so tragically underutilized.
9. Mihawk
I used to like his character a lot more than I do now. His serious shtick was a nice change of pace when he was introduced, but at this point, I just consider it unappealing. A fight between him and Zoro wouldn't feel personally interesting to me; it would just be another box to check. Thus, I rate him really low.
10. Weevil
I think everybody was a bit disappointed to see Whitebeard's biological son finally. And moreover, that's all you can really say about Weevil. I will give it though, that at very least, Weevil's existence properly set the stage of expectations for how surprisingly good Yamato turned out to ultimately be.
11. Hancock
Hancock, honestly, feels like little but a walking trope. Not a person, real or fictional, but simply a trope. Honestly, I don't like either her or the result of her story arc. She fails as both a justified ally and a satisfactorily defeated villain for me. Moreover, she's one of the most wanked characters on this platform. I've got to put her on the bottom for now.