Ok, this needs clarification. The entirety of the 4th generation is powerful (being sired by the Antediluveans), but on an individual level, they vary in both mastery of their disciplines and their personal skill, and that applies to even their starting disciplines. Take for instance Menele and Enkidu of clans Brujah and Gangrel respectively: Menele has advanced Celerity up to the ninth level while Enkidu has done the same with Animalism, but how much they've mastered their other disciplines varies anyway.
I'll get to the point: which member of the 4th generation is the most powerful vampire in said generation? To narrow down the possibilities, 4th generation vampires who attained the power via diablerie or those who have met the final death aren't up as candidates, and those who have diablerized members of the 3rd generation aren't candidates (since they aren't 4th generation anymore).