Just gonna say, I am solely here to discuss Skill between these two character's. I am not really here for the other aspects of the match, as frankly- Nasu Hax vs KH Hax is not something I feel confident about getting into.
That said, the best feats I can really find for Nero are the aforementioned defeating Sun Amped Gawain, and being evenly matched with Cu Chulainn according to Rin Tohsaka, who tends to be a very reliable source in regards to all sorts of subjects in verse, including Servants. That said, while this is impressive, 1, we don't know how much Nero's own stats may have played a factor here- Take into consideration the fact that Saber Classes are notoriously stated to be the perceived best class in the verse, as well as the fact that Lancer's are often shown to be weak against Saber's (Though that whole Class Weakness Chart never always applies). Even so, unfortunately, merely scaling above other character's in Skill often isn't really considered substantial enough on this site (Trust me- I tried these very same kinds of arguments before).
I also see that there is a attempted argument for Nero being > A Supercomputer via the fact that Shirou can maintain a reality Marble. But, even if we take the idea that maintaining a reality marble is of this caliber, there is nothing indicating any scaling above Shirou for Nero, and in fact, I would argue that at least in UBW, Heaven's Feel, and Oath Under Snow, Shirou would massively dwarf Nero in skill (Via the simple fact he's been copying the skill of numerous much more skilled Servants and has been shown to maintain that skill for a seemingly indefinite period of time after copying them), so this argument doesn't really work. If the Argument here is that her Noble Phantasm is a Reality Marble, ergo the same idea applies, the fact is that her NP is not a Reality Marble, but rather it works similarly to one. Instead of overwriting the world, it merely builds on top of it- Which is something a Computer can likely quantify rather easily, or at least would be much easier to calculate.
In any case, while I do find Nero impressive if we take into consideration Skill Scaling, Sora simply has wayyyy more feats to his name. There's the fact that he can parry a Omni-Directional Laser Attack, for one- Or maybe the fact that he consistently is shown being able to pick up New Weapons (Primarily through Formchanging) and is able to use them with surprising skill in spite of seemingly never having trained to use them before. Or how about we use how Roxas (Who as his nobody, should have comparable/equal skill to Sora) was able to defeat character's like Saix and Xion in spite of working off of essentially fumes (Xion was absorbing the vast majority of Roxas's power at the time, yet he still defeats these combatants who should explicitly dwarf him in sheer stats.). Sora simply has way more going for him overall, whereas most of Nero's best feats are just fighting other character's normally, which while impressive, can be heavily affected by her stats, whereas a lot of Sora's stats don't matter for his feats or feats he scales to.
