This list can only cause endless pointless debate, since the strength of some of those characters hasn't even been revealed yet.
If I have to arrange them in a list, I would say:
I put Mihawk at the top, since he is the greatest swordsman and Shanks' rival. If old man Rayleigh, who is far from his prime can handle Kizaru, I am pretty sure Mihawk in his prime can do it as well.
Then Enel and Kizaru are both about equal, since their DF powers are similar and enable them to travel instantaneously and have devastating ranged attacks. Enel even has his mantra which would be a great advantage. He was just really really unlucky that he got Luffy as an opponent.
Magellan has proven to be a beast, which no one without ranged attack or haki can beat (if haki really can resist poison or something like that).
Blackbeard can totally devastate most Logias and has extreme endurance and strength. He would probably be higher on this list if he did not get so easilly defeated by Magellan. He could probably still beat Enel/Kizaru though…I don't know
Kuma and Aokiji are pretty strong overall fighters, especially Kuma has a variety of interesting abilities.
Croc is pretty much a generic Logia user - most of his power comes from being invincible. However, water is not that hard to come by, so he is not near the top.
I don't have much to say about Moria...
Sentomaru is just a haki user, which is good, but the only thing he did is fight about evenly with an extremely distracted Luffy. He is way overrated!
Lucci is insanely strong, but pretty much everyone else on this list can defeat him...