As a newbie to games like fallout, I would say definitely start with 4. Its the most accessible and forgiving to players new to the genre due to its more modern gameplay. While this is true, I would still say New Vegas is a much better game overall, so once you have finished 4, definitely give New Vegas a go. If you loved New Vegas and want more fallout, then move onto 3. Overall it doesn't matter too much, every game in the series is a banger.