Depends on the subreddit, but unless it’s an entirely opinion-based community then I prefer an objective summary or nothing at all. If it’s a news subreddit, for instance, I want the article as the main post and if you have an opinion then put it as a comment. This goes for text posts too, I get annoyed when people make Ask Lemmy threads with their own answer in the main post.

My main problem is that it transforms the thread from being about the link (or question) to being about the OP’s specific opinion, because they are inextricably linked and there’s no way to respond to their opinion without making a top-level comment. If the OP simply left an opinionated comment instead, it could have a proper discussion thread like every other commenter, preventing the top-level comments being flooded with replies to OP’s opinion.