Trafalgar D Law is the best SN. He has the best development of the SNs by far, from a D with hax devil fruit, backstory with the Donquixote pirates, while being in an alliance with the SHs
After that i'd say Capone surprisingly became very likeable especially after the events of WCI, where his mafia style and gangsta attitude was very entertaining to watch in the plan to try to take out Big Mom
Kid has less development so far, but i'm not worried about him due to Oda saying he was the one he was aiming to be the most important one when creating the SNs, so i expect his development to reach his peak this arc, and with Killer as well
Hawkins and Drake are good arc potential as well imo. In Hawkins case, due to his potential character development around card games and abilities, but it could depend on the way Oda will go with his development in Wano. For Drake due to his backstory around the marines, while being undercover in yonko crew
For Bonney, she has a shady past with the world government, with a devil fruit that may potentially be linked to gorosei, backstory related with some of the most famous pirates of the world of one piece, leaving you think she has good potential as well
Urouge is good for his memes, his off-panel actions(beating Snack and so on)
Literally i think all of them are good, with good potential. The only one i don't care about is Apoo.