NCR is probably the best of those. They're hardly perfect, but since they're democratic, they have a decent chance of improving their policies over time, plus, even as they are now, they can provide a certain amount of stability once they've firmly established themselves in an area and allow their citizens a workable level of personal rights. The Legion, on the other hand, are just evil, savage, and backward-thinking to the core, with the only thing they have going for them being the stability they'd offer to the few people they didn't murder or enslave. Brotherhood of Steel would probably be even better than NCR, but they're way too isolationist to be of any good. Followers of the Apocalypse are also nice, but they probably wouldn't have the stomach or the resources to provide security and stability. After that, the Enclave is insane, House is too controlling, and anarchy is just terrible for everyone. NCR wins, hands down.