I'll be buying the Collector's Edition (once it is announced) on Xbox One. Mainly because I played the other games on 360 and I'm partial to keeping my gaming history/achievements on Xbox Live. Also, by the time the game is released Xbox One to PC streaming should be available, so when the TV isn't available I can still play through my PC. I'm also a purist who prefers the vanilla experience to begin with, and don't care too much about graphics in a game like Fallout. Later on I'll inevitably buy the GOTY edition on PC. I might even grab it on PS4 once it hits bargain bin prices. I usually somehow end up buying all Bethesda games at least 3 times over
Also, in the very back of my mind I know Bethesda has a history of favoring the Xbox and they used it as the lead platform for Fallout 3. You'd always see them using the 360 controllers in their demos. DLC came out first on 360/PC. With the PS4's popularity and the similarity in architecture hopefully we won't have a repeat of last gen's problems. Xbox One might even end up being the version that suffers because it's the least popular now..who knows. Still, Xbox is where I'm starting out.