Use the population checker at the bottom of the main page of this forum. Late night(for me) tends to have a low population with it rising to 100+ as time goes towards morning and beyond.
You are new so heres a quick lesson: PKing(read: Death) is prevalent in unguarded towns and with the guarded towns spread out so far, NCR is a bit of a hub for social interaction. Go there, you Will see people eventually depending when you look. The crowd hangs at the front, where the bombers, thieves, and "Shitinmouth" people tend to hang and harass whoever they feel like.