My overarching caveat is that it comes down more to how good a fuck the guy is than size - I've been really, really well fucked by guys with average sized dicks, and really poorly fucked by guys with big ones (and vice versa). That said, I do generally prefer guys with at least bigger than average cocks in both length and girth; I love the full feeling of being opened up and stretched and getting my hole deeply used. The fuck from a large cock feels more intense and sensual.
Also in my experience (and this may sound counter-intuitive) but if I'm about to find out that a guy is a bad fuck (lol), a bad fuck from a guy with a bigger cock is not as bad as a bad fuck from an average sized guy. That's a super generalized statement, but usually for me a bad fuck (as opposed to a boring fuck which is what it is but is fine) involves pain and/or a lack of concern about said pain. I'm significantly more likely to feel pain (like "ow, jesus!" pain) shallower - the region between my hole itself til just past my prostate, so if it's being caused by a guy with an average sized cock it's going to be non-stop.
Two of my favorite regular fuckbuds (pre-COVID but we're looking forward to getting back together) couldn't be more different in the cock department - one has 8 thick inches and the other is textbook average in length and thickness. And I always have a freaking fantastic time with either of them, they're just very different kinds of fucks. But both are GREAT fucks and both make me feel amazing, happy, and well fucked afterward.