discussion should be used if you want to discuss about an on-topic question with other users (e.g. "Should down-voters explain why they down-voted a post?"); if you are suggesting a text change because (for example) it doesn't follow the English grammar, or there are repeated words (such as "flagged posts for for kiamlaluno"), then I would use bug; if you are suggesting to change the text to give more information, or information that is more pertinent for the user in the given context (e.g. replace "You need at least 2k reputation to review Suggested Edits." with "The suggested edit is pending review."), then I would use feature-request.
For what I understood, support should be used when you don't understand how a feature works, or when you are asking a tag synonym, a tag merge, or burninating a tag. If you know that something should work in a way, but it doesn't, then you are reporting a bug; if you are not sure how a feature works, you should use support.