this means spoilers
In my opinion, my favorite Fallout game is Fallout ; New Vegas. From my steam review I say little, to nothing, But I believe its because there is nothing that needs to be said. I'll begin with the fact its different. Its very un-traditional because of the fact that it involves a post-apocalyptic mailman. Compared to the other games, you start off in a vault, or being involved within a vault (Excluding BoS and Tactics, but I really don't consider those Fallout games for a complicated reason). Secondly, my other reason its my favorite is because it has a more RPG feel to it, it has the classic feel of that your decisions matter. As I saw when I was playing Dead Money, the way you treat your companions matters because it determines if they are friends or enemies. my example is that I told Dean Domino I was going to break his legs if he didn't stay there and do what I told him had an effect on an outcome of Dead Money because you had to kill him or persuade him in the end. Third, and lastly, is the main story. As I said in my last few sentences, your decisions matter. Being that you massacre every NCR troop in Camp Searchlight just because you wanna makes it so you can't really do quests involving the NCR as an ally. I chose Caesar's Legion on my first playthrough so I learnt this the hard way. Those are basically my reasons for why I think Fallout ; New Vegas is the best Fallout.
Thanks.