That's an interesting question: what's worse, Fallout 3 or Fallout 4?
While neither is very good, obviously, I would say Fallout 3 is significantly better than Fallout 4 for the following reasons:
1. No "daily grind" quests/gameplay: Quests, shitty as they mostly were, were hard coded, so at least it felt like you were making progress. In F4, you keep getting these "free settlement A" or "defend village B" or whatever quests without end that mean absolutely nothing. You just go somewhere on the map, kill some enemies, and come back for an XP reward. Sometimes these even repeat, so it seems they are just some sort of shallow procedural bullshit. Once I saw them start to repeat, I just ignored the rest of them, and it had zero effect on the game, as far as I can tell.
2. Actual dialogue: F3's dialogue might have been not very good, but at least it felt like RPG dialogue. In F4, that dialogue wheel abomination killed whatever shreds of dignity the game had left. It felt especially retarded at what were supposed to be dramatic and emotional moments. For example, when you discuss your dead wife/husband and the dialogue wheel gives you these short speech summaries like "wife ded" or "kid lost" or something along those lines. Utter cringe.
3. Better rpg system: self explanatory.
4. Slightly less cringy writing: Obviously F3 is no champion of good writing/lore, what with Little Lamp and Republic of Dave and other bullshit it had, but Fallout 4 took the cringe to the next level. Almost everything in it is cringy, writing wise. F3 at least had some percentage of content that felt serious, in F4 this is very rare.
5. Circus looking world: F3 felt like a desolate wasteland. F4 world feels like a circus set within a desolate wasteland. Everything is too shiny and colorful and weird.
F4 did have somewhat better combat, but that's about it, and so F3 > F4.