Anyone want to explain their choice.
I'm trying to do a "good" playthrough (typically doing whatever rewards good karma or whatever is best for the wastes, so for example I WOULD kill off the NCRCF Powder Gangers in the Mojave, but perhaps not the BoS) so I looked up the two endings and compared how each group felt with each ending. In the end, I decided that even though fighting was more practical, evacuating was better. Everyone can end up at least partly satisfied with the evacuation ending, whereas fighting leads to a couple rocky issues in the future.
I also argued that, if you compare what Caesar did with the Blackfoot tribe to what Graham wants to do with the Sorrows, it's practically the same. He's taking a losing tribe that's under attack and reforming them, teaching them the ways of combat. Since the theme of the DLC is pretty much the Bible, the general feel I got was "Violence begets violence" and in a less biblical sense, "those that don't learn from history are doomed to repeat it." I decided it probably wasn't a good idea to let Graham walk down the same path he'd already walked down, let alone one simlar to Caesar's.
Nevertheless, I must admit the endings are well done. Though I'd be willing to argue that evacuating Zion truly is the good ending, you leave VERY unsatisfied if you do it. Things just don't feel finished, probably because you don't get to see the benefits of your choice (quite the opposite, the White Legs control Zion), Zion as a location turns into a hell hole (no friendly NPCs, but plenty of hostile White Legs and mutated animals) and you don't feel as though you've gotten closure. You have no idea how the Sorrows are doing, no idea what became of Graham (you don't even get an ending slide for him if you evacuate. They probably purposefully did that to intentionally give evacuaters no sense of closure) and the White legs seem just as strong as before.
On the flip side, you can fight the White Legs and get more practical rewards and a more practical good ending, but at the cost of turmoil starting between the Dead Horses and Sorrows in the future (which you don't see in game, but yeah not exactly a "good" ending), and being single-handedly responsible for Daniel basically hating himself.