Fallout 4 would be my choice. So much content and gameplay hours in that game and so many different ways to play it.

If they ported Fallout 3 or Vegas I would hope they would spend the extra time to update the graphics to a much higher standard maybe like some of the PC mods you see or close to Fallout 4 level even if they have to reduce draw distance a little and drop some complexity from the engine the same as LA Noire I guess. On a small portable screen I don't think draw distance is quite as important as a large tv screen I think you are more focused on the foreground anyway. I noticed playing ps4 games on Vita that you miss a lot of the minor background stuff as its just not visible in the same way.