Help on use of ことが and のが when nominalizing a verb

Hi all,
I'm wondering if there's a rule that helps to decide when to use ことが or のが to nominalize a verb.
It seems to me that it depends by the verb that follows, so that for 思い、言う、好きです I have to use ことが, while for all the other verbs I have to use のが.

Is this so simple and correct? (I doubt actually)…
Thanks!