We've seen lots of rulers on the many islands of One Piece, be it kings, chiefs, leaders, or mayors. The main rulers are:
4 Blues: Woop Slap, Boodle, Genzo, Wapol
Paradise: Nefertari Cobra, Nefertari Vivi, Dalton, Gan Fall, Shandia Chief, Boa Hancock
New World: Neptune, Riku Dold III, Gancho, Inuarashi, Nekomamushi, Elizabello II, Ivankov
Which are the best island rulers / kings in your opinion? Who is the most just, the most capable of leading an entire country?