i would really like to say itachi but that would be biased and i just noticed you typed "currently in the manga" so i would say naruto! sasuke comes close of course.
maybe the undead itachi that kabuto ressurected kidding
Right now it must be Mandara until Sasuke Masters His New Eyes and Naruto Masters The Fox, then it be up to Sasuke and Naruto to show the world ones and for all Who is the strongest Ninja their is.
It would have been the sage of the six paths but currently it is madara which will be replaced by sasuke when he can master his eyes which would then be replaced by naruto when he masters kuubi.
Kabuto. Assuming that the corpses he controls have most of jutsus that their original counterparts did and apparently he has more that he can pull out.
It all depends on what you define as power; in terms of raw power it has to be Killerbee as he is one of the few who has the compleat control over his tailed beast; and Kisame who fought him and manage the to infiltrate the village comes very close as well.
In terms of talent it has to be Uchiha Sasuke, he is just 16 and already has EMS.
But the most rounded shinobi in terms of a all aspects is Uzumaki Naruto
i would say between naruto and sasuke. sasuke may sab madara in the back as soon as he has learned all he needs to know eliminating him from his quest of vengence. naruto is going to learned to master the nine tailed fox making him equal with sasuke will be a battle bigger than the valley of the end to find out who's the strongest.