I can't understand siding with the Legion unless you are playing an evil character (maybe "Lawful Evil", since they bring law and order of a sort). They take slaves, and they crucify people alive for things as minor as drug dealing. Plus, women treated as second class citizens.

The NCR means well, although they are a large democracy with all the corruption and politics such brings. (Democracy being the worst form of government except all others that have been tried from time to time, if you will.)