I'd say a Lucifer would last longer, as it isn't vulnerable to precision attacks (ie bomber strikes to the engines and weapons). Also, it is far smaller than the Sathanas (less than half the size) but has 80% of it's hitpoints (800k compared to the Sath's round million). That means it's far harder to find, but almost as hard to destroy. It's offensive firepower, while not as potent as the Sath, is still vastly superior to any GTVA vessel, so there isn't much that can present a serious threat (except maybe a group of several destroyers, maybe a pair of Orions plus a pair of Hatshepsuts would manage it, if they could destroy enough subsystems (engines first, then beams and reactors) quickly enough, but the losses would still be significant.
I think the lack of bomber support would prove critical. The Sath is a more dangerous individual target, but the Lucy's superior durability is key - without bomber strikes to soften it up, capital ship attacks are more difficult as the target is at full strength to begin with (as opposed to being damaged and possibly slowed down). The Sath can be reduced to an effective hulk by a few bomber wings, leaving it as target practice for the capital ships sortied to finish it off.
Much more importantly, however, the Lucy is so much cooler than the Sath in every possible way. So it gets my vote purely on that basis.
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