Fallout 3 or Fallout: New Vegas on Xbox 360?

I want to get one of the 2. I heard Fallout 3 is pretty good and better than New Vegas but I wanna get New Vegas because there are more options and things. its basically an upgraded fallout 3 on a new map. I would like to have as many options as i can so thats y im leaning more on new vegas's side. but what are all the differences between the 2? plz answer and help me decide and plz tell me in your opinion only if u have both games and i am completely new to the series i just got introduced a few days ago so keep that in mind...