Skyrim was already a downgrade next to Oblivion, and the latter has aged so poorly that it's nothing but memes nowadays.

Both I'd say.

Skyrim for it's exploration and OST.

Witcher 3 for it's engrossing environment details and some of it's combat (even though it's sword play reeks of Souls inspired).

Quests from both games largely feel the same (even for other RPG's and MMO's out there).

The Witcher 3, by far. The base game but probably edged out Skyrim, in my opinion. It's just better gameplay in general, and significantly better storytelling.

But, when you add in The Witcher 3 expansions, that puts the game way over the top. that second expansion to The Witcher 3 is probably the best expansion of any video game that I've ever played. It was as large as many whole games, and it was beautiful and well done. When you add in all that, it puts the Witcher 3 in probably my top five, definitely my top 10 games of all time.

Witcher 3 for me. Skyrim's glitchiness was a turnoff to me, and as others have said, Witcher 3's combat is better.

TW3, easily so. The writing is great, as is the voice-acting, TES games are notorious for their poor writing and VA.

Quests are on another level; Skyrim quests are basically run to the quest marker, slay everyone in the dungeon, go back and get ten gold pieces. Motivations, characters, and objectives are all stylized and shallow. Almost all quests are variations upon the same thing, over and over. One plotline that could have been interesting with more depth and breadth is the civil war. Not only does it play out in a ridiculous and tedious manner; the choice you make has almost zero impact on the game itself and its world. Choices don't matter, which makes the choice worthless to begin with.

Skyrim's combat is completely without weight and feel, it's a rock 'em sock 'em simulator with poor sound design on top. Enemies have very little variation, and their AI is shoddy at best, hilarious at worst. There's also no strategy to the fights; approach and whack until dead, or sneak and loose arrows until dead (often a single arrow). 

One area where Skyrim shines is atmosphere, and the brilliant music does it a service as well. The problem is the world itself, it seems anemic and dulled down, characters are flat caricatures of people and no one shows signs of proper intelligence. Convictions are all childish rage and simple need-to circumstances to drive the plot. It's just poor design. Especially cities showcase this issue, characters are either sitting around eating and drinking all day or standing/walking aimlessly around the streets, tossing nonsense at you as you pass them by.

With a bunch of mods, Skyrim is still a great game. But the changes made to appeal to a broader audience are the very same that alienated it from fans of the older TES games, and indeed the RPG genre as a whole. For me, there's no contest here, and while they are different types of games, one could argue that the essence of the TES series is a direct competitor to TW3 and its core design. To say that they're too different for comparison is too easy, in my humble opinion. It's not Trackmania vs Gran Turismo.

I've played a lot of Skyrim, and a lot of TW3, the key difference is that my two playthroughs of TW3 were one continuous stream of being engrossed and captivated by the world and writing and characters. Skyrim, on the other hand, I've found myself making at least 30-40 characters, and I've only ever finished the main plot twice, it's just not tempting and captivating. There's not a single character I ever cared about at all. I always find myself bored after a given number of hours, when I realize that my choice of "build" makes no difference either. Which race I pick has no proper bearing on the gameplay, only a few snide comments coming my way from time to time, and skills and weaponry and/or spells and magic is built such that everyone can always get equally good at everything. 7-foot orcs can pickpocket and sneak like 5-foot wood elves (and the wood elf can smash with a warhammer in the exact same fashion as the orc), Argonians get the same prices in shops and taverns as Nords and Imperials, everyone can use magic, everyone can dual-wield and wear the heaviest armor, and even forge this themselves. Same sprint speed and jump height, same carry limit, stamina, health, and mana. All the seeming choice in the game has no effect, and thus very little point, besides cosmetic ones.

Witcher 3 but Skyrim is great too. They both offer very different things.

Skyrim is more make your own story. The actual story is such a small part it feels more like a side quest. The real content is in all the amazing things to find. TW3 is more live someone else's story with a bunch of distractions keeping you busy.

To me Skyrim has far more imagination and variety which keeps me interested. TW3 has a much more narrow focus, good for keeping you interested in the main story but not to keep me interested in the game in the long run.

I couldn't get into the witcher, but I've spent like 200hours in Skyrim.

Some of the Witcher 3 problems imo, handholding with a story that didnt draw me in as especially interesting or unique, I find it awkward to control Gerald whereas Skyrim in 1st person felt natural, Witcher 3 felt kind of ugly to me whereas I love the design and landscape of skyrim in 2011 and still find it easier on the eye than many of Witchers 3 more realistically rendered but less appealing locations. Lastly Skyrim immediately pulls me in with the character customisation and atmosphere.

Im bias because Oblivion really sold me on the elderscrolls universe but even that took like 3 different attempts before I actually got into the game. I'm hoping to give witcher another shot later this year

Playing Skyrim is like ordering a pizza. You can have em put whatever you want on it (even if it's some outlandish combination of things), get it in various sizes, you can save half for later and it eat it cold...whatever. It's Pizza. It's always gonna be pretty solid.

Playing Witcher 3 is like going out to a really nice restaurant. You're gonna get dressed up. There's gonna be a limited number of dishes to pick from, but everything is gonna be absolutely top quality. The menu is designed in such a way that everything synergizes, and stimulates your palate a certain way. You're gonna be there with others, whether it's family, business partners, friends, or a date, and have a lot of engaging conversations. It's a whole experience.

I choose Skyrim.

I love exploration and doing what I want, going blind into skyrim felt amazing, it has a lot of small things I found out and enjoyed.

Meeting a giant for the first time who one hits you to death and let you fly all the way to Black Marsh, find a cave that leads to a Dwemer cave that ends up in blackreach and then finally find out you spend 6 hours today in one cave.  Make a house, get married and have children. Find a blind bandit who reads a book, steal the book and find out that their is no word written in the book it is all optional but only adds more value to the experience.

The story can be described as boring but their is so much lore and so many books to read it all depends on your choice and I prefer it instead of following a long story that I hardly enjoy.

Sure the civil war can be dissapointing and I enjoy when people who played the game for hundred of hours find out that a Truce was also possible 

Sure the games after daggerfall became more simple but I am fine with it.

A game like Daggerfall with the graphics/gameplay of today seems impossible.

Daggerfall was to hardcore for me, accepting a quest to bring a potion to a sick person and failing it because you explored some caves/villages and the person died from his sickness is rather annoying.