The rest of the CVBG is unrepping for fuel every 4 days so there is little benefit that the CVN doesn't have to too. A conventional A/C carrier can sustain much more battle damage and still propel itself than a CVN. For that reason alone conventional is much better.
That is in the realm of theory. A nuclear A/C has never been damaged in combat. So you are speaking theoretically, not based on actual experience.