From what I have seen, Reels still tend to have the strongest discovery potential because Instagram can push them well beyond your existing followers. That said, I would not ignore carousels, especially for educational or highly saveable content, since they can sometimes generate stronger engagement even if the initial reach is lower.
Have you noticed whether your Reels are reaching mostly non-followers or your existing audience? I ask because that is usually the clearest sign that Reels are actually helping with discovery.
Also, what kind of content are you posting? I ask because the best format can vary a lot between entertainment, education, personal brands, and product-focused accounts.