While I have near infinite love for both, Fallout takes the cake.
Elder Scrolls has beautiful words, great lore, and is of the few (In my opinion) good western RPGs.
Now Fallout, don't get me started.
First, fantasy/midevil has been done so many times, but the Wastes just feel... Different.
While the new Fallouts have lost their roots for the most part, they are still good. Fallout 1 was great, and Fallout 3 was great, though they're completely different genres.
Every Fallout game I've played, I love. Roaming the Wasteland, jamming to 50/60s music while blowing the head off of a Super Mutant with my plasma rifle, Versus, I stabbed my sword through the chest of a Frost Troll, and then finished him with my fire spell. Which sounds more unique?
I also like the lore of Fallout more.
You take your first steps out of Vault 101 searching through a post-nuclear apocalyptic wasteland. A ruthless, unforgiving place where the people are either savages or crazy. Finding a brand new water purification chip, searching through a hellish desert, looking for a small piece of tech that brings tonnes of lives into your hands with the threat of dehydration.
Versus
A giant dragon descends from the heavens, threatening an entire countries existence. You, the Dragonborn, are the only one capable of defeating him, with your Dragon Shouts.
They both sound incredible and unique, but I just prefer Fallout. Don't get me wrong, I adore both immensely.