Not just rarely, never. There are very few cases where "which" (in that sense) is used alone, and that isn't one of them. In fact even "Which would be used?" is something I wouldn't say; I would say "Which of these would be used?". The only case I can think of where it would be used alone is in quick, terse expressions such as "Which do you prefer?" or "Which is it?".
To be clear, "Which would be used?" isn't really bad per se, it's just one I wouldn't use personally.
If you're going to change it, you should make it "which ones", because "which one" implies that you think only one choice is correct. I would actually say "which of these", though, because "which ones would" is difficult to say.