rather than, as opposed to, and instead of

i want to swim instead of walk. i want to swim instead of walking. (????)
the first sounds more natural to me, but I've heard you can only use instead of with -ing construction. is this true?

i want to swim rather than walk. i want to swim rather than walking. (????)

i want to swim as opposed to walk. i want to swim as opposed to walking. (????)

Thank you.