Question: So [Sawa in another thread](https://japanese.stackexchange.com/questions/5876/how-do-you-say-you-have-gotten-better-at-x/5880#comment14949_5880) says that こと cannot be used in the example below. Even though it performs the same function as の (as far as I can see). 

> 
> 料理が(前より(もっと)) {上手だ/上手い/上手になった/上手くなった}
> 
> 
> **料理するのが**(前より(もっと)) {上手だ/上手い/上手になった/上手くなった}
> 
> 
> **\*料理することが**(前より(もっと)) {上手だ/上手い/上手になった/上手くなった} 
> 
> 
> 

So what is the difference between the two that one can be used but not the other?

Answer: 
The difference is difficult and the linked question gives a decent explanation, but here is my two cents:

When you use `料理するのが`, it immediately feels like there is a direct actor involved. If you look at all the examples sentences in the link, when you use `の`, it puts a focus on the fact that somebody is performing the action.

However, when you use `料理することが`, the focus is no longer on the actor involved, but the *action itself*. If I would translate the third sentence into English, it sounds to me like the following:

> 
> The act of cooking has become better.
> 
> 
> 

I realize that the above sentence is unnatural English, but my point is that the difference between `の` and `こと` is whether the focus is on the actor or the action itself.

However, my above explanation *might* not fit every pattern, so I would take this as general advice. For example,

> 
> サッカーを見ることが好きです。
> 
> 
> 

In the above sentence I am using `こと` even though the act of "watching" has a direct actor involved. I believe the reason why `こと` sounds better here is because the act of liking is focused on the `サッカーを見ること` which is the focus of the sentence.
It's a very rough and shallow answer, but:

* こと is a concept/an idea.
* の is a tangible thing.

You can be good only at doing the tangible thing. It's meaningless to be good at an idea.

Just remember that with "上手だ", it's "の" that works for the reasons I mentioned. With other "verbs," more complex explanations may be required, and have partially already been discussed here.