I've just learned to nominalize verbs with のを but as I was looking for more info on the web I saw that this is also done with のが and こと. The question "What is the difference between the nominalizers こと and の?" uses のを and のが as if they were the same thing but does not explain if they can be used interchangeably. Can they? What's the difference?
水{みず}を飲{の}むのが好{す}きです。
水{みず}を飲{の}むのを好{す}きです。
Flaw's answer is of course correct, but here's another way to look at it.
Start with a simple sentence like this:
犬{いぬ}が好{す}きだ。 "I like dogs."
Since the predicate is a na-adjective, 好きだ, the object (犬) needs to be marked by が. (Your second sentence is ungrammatical for this reason, btw.)
Then, if you want to say something like "I like running.", you need to change the verb 走{はし}る into something like a noun, so it fits in the same spot as 犬. You do this with 〜の. This is essentially the same thing as "run" → "running" in English. So, we get:
走るのが好きだ。 "I like running."
If you instead have a predicate which requires an を-marked object, like やめる "to quit"/"to stop", it goes like this:
会社{かいしゃ}をやめた。"I quit my job."
走るのをやめた。 "I stopped running."
Basically, all the 〜の does is make a verb act like a noun, and then syntactically-speaking, that noun-like thing can fit into any spot a noun would normally go, and that spot will already be marked with が, の, or some other case particle.
The nominalisation occurs with just の.
を and が are case markers and the choice between them depends on the other part of the sentence; whether a verb that assigns a を argument is used, or a verbal nominal adjective (such as 好き that takes が for object marking1), or a stative clause.
Verb: 宿題をするのを忘れた
Verbal Nominal Adjective: 水を飲むのが好きです
Stative verb: 誰かが話すのが聞こえる
[1] The Structure of the Japanese Language, p. 91, Susumu Kuno
