Fallout because TES is horribly designed. I had fun exploring Morrowind, Oblivion, and Skyrim, but when it comes time to make progress in the game things turn to shit.
First, the story is laughably generic fantasy. I don't even wanna hear about their supposedly brilliant fourth wall breaking narrative. It's a gimmick to explain save files, nothing more. Not only that, but you wouldn't even know about it unless you read through the thousands of books scattered around those games. I always want to read every book I come across, because I don't like to think I'm missing out on anything in a game, but Jesus, they're so fucking boring. If I have to read the equivalent of War and Peace in terrible fan fiction style history tomes just to understand what is honestly, a very simplistic story, count me the fuck out.
Second, level and mission design in TES are some of the dullest in gaming. Skyrim was a bit of an improvement over Oblivion's identical procedural dungeons, but let's be honest, Skyrim's dungeons got real boring after the first 20 or so. If I had a penny for every Draugr I killed, well, I could buy a better game. In Fallout 3 and New Vegas, almost every scenario you ran itno was unique in some way. I also liked that Fallout's quests tended to be focused more on interesting character interaction. There were a handful of interesting quests that I came across in Skyrim, but mostly it was just "kill all the Draugr/vampires/Dwemmer/bandits/Imperials".
Third, I like Fallout's sense of context. By that I mean, in Fallout 3, I really felt like I was part of that world. I consider the intro to Fallout 3 one of the best in gaming. In New Vegas, I really felt like I had different relationships with each faction. In Skyrim, I never even bothered to join the Stormcloaks or the Empire, because neither of them are in the least bit sympathetic. Moral complexity shouldn't be about making everyone bad so much as making everyone understandable. Fallout got this. As horrible as the Legion seemed at first, once you got to know Caesar and some of the other leaders, you can understand what they're trying to accomplish with their brutality. And that was the most extreme example. The Boomers, The Khans, Mr. House, and The Brotherhood of Steel all had legitimate reasons for fighting, and were all sympathetic. Skyrim's pointless civil war and soulless NPCs just made me want the dragons to take the place back and roast the entire population.
tl;dr, I like Fallout's more tightly structured narrative over TES sandbox style gameplay. I like fewer, unique scenarios over tons of generic scenarios. Depth over width, I guess.
