The 2 best imo are mihawk and jinbe hands down.
Most of the warlords have a great skill set and some pretty unique abilities, not all have a great personality but they're not all expected to align themselves with our protagonist or even play as big of a role. Kuma and Hancock are 2 more that I like to an extent, Kuma is becoming more interesting as time goes on and Hancock has a great set of abilities that match her character very well as the character who is famed as the most beautiful woman in the world