I had answered the question about this on the ELU site. I am taking the liberty of reposting my answer here:
The trick to knowing how to use; of which, at which, in which, to which, from which (etc.) is to analyse the prepositional phrases, phrasal verbs, verbs and prepositions in a sentence and then see how it can be transformed:
He /spoke of/ war and peace and many other topics that day. The topic
/of which he spoke/ was complex. The verb here that means to speak about a topic is /to speak/ of a topic/: to mention
The party /at which/ he spoke/ was noisy. Phrase: A party is held /at
a place/. It is implied.
The situation /in which/ we found ourselves was dire. Phrase: /to find
oneself /in a situation.
The bonds /from which/ we broke free were tight.
phrase: to /break free/ from bonds.
The town /to which/we were driving was 50 ks away. phrase: to /drive/
to a place.
Summary (and not a complete answer but a general one): The preposition depends on the verb that takes a preposition, a phrasal verb that includes a preposition, or it depends on the prepositional phrase used. Also, there are many other prepositions that can be paired with which: under, during, about, over, etc.
Best Answer
Both forms are accepted, although if you're still learning, and didn't make it a habit, the '-ing' form is less ambiguous.
The problem is that the 'verb to verb' in some contexts may mean two different things.
It means unambiguously that I don't smoke (cigarettes or whatever) any more.
And here we don't know: was the decision to stop smoking? Or - conversely - he stopped raking leaves, in order to smoke a cigarette, and then, while smoking, came up with the remaining decisions.
In other words, the negatives - 'stop', 'pause', 'cease', etc connected with 'to verb' may relate either to stopping/pausing/etc that specific activity, or pausing a previous activity, in order to start the given activity!
The '-ing' bears no such ambiguity and is equally valid as a grammar construct, so if you have no specific reasons for writing otherwise, '-ing' is safer.