I get a bit bored of the environments of Fallout, and I'm so used to guns from shooters that I find it a nice change to go swords and magic in ES. Both excellent franchises though.
Question is not clear enough. Fallout 1 & 2? Hell yeah, all the way, still playing both and will be till the Kingdom Come.
But Fallout 3? I'll stick to the Oblivion with swords in this one, just because F3 is ugly as shit, even if it has it's great moments. How is it that F1&F2, even with their old 2D isometric engine could have terrific locales, well thought out enviroment and variety? NCR doesn't look anything like the Den, Junkyard is so much different than Boneyard, and Glow or Sierra Army Depots are great examples of designing with style and atmosphere. In F3? Almost every settlement looks exactly the same, and ruined Washington (especially metro stations) is just boring as hell. Oblivion at least differentiated it's vistas a bit - snowy mountains here, some green plains there, and cities were pretty distinct in architecture. The only locations I fondly remeber from F3 and which stand out are the Oasis, "newbie town" Megaton and Tenpenny Tower. Mybe you can count DLCs as something new, but still, first impression is not nice. Especially when you compare it to the awesomness of comparing backwatered Shady Sands and Brotherhood's bunker. In F3 such contrasts are not well presented, even the Pentagon looks like some shitty mall you find near Megaton.
I don't know how anyone can prefer Fallout over Elder Scrolls, but that's just me. I struggled to do absolutely everything possible in the fallout games to cap over 100 hours on my playthroughs, Elder Scrolls games I barely had a problem considering I could at least warrant a reason as to running through the game multiple times along with their seeming to be more to do.
Gotta go with Fallout 3 myself. The post apocalyptic wasteland, vats system and different weapons and people I loved. Environments got quite boring though, too many subways and brown wasteland everywhere. Oblivion I have never finished. I hated doing the Oblivion Gates, thought they were all terribly boring, and hate the combat mechanics and utterly ridiculous levelling system of the game.
They both are awesome games for sure, and its hard to rate them against each other because the one I play when I want a sweet open world RPG with guns and the other when I was a fantasy version. But if I had to pick I would probably go with The Elder Scrolls, I just like the area and lore behind the elder scrolls.