Midjourney provides better results out of the box, with Stable Diffusion you need to know how to use custom models and/or LoRas to get similar or better results

Midjourney provides better results out of the box, with Stable Diffusion you need to know how to use custom models and/or LoRas to get similar or better results, plus Midjourney does not allow you to generate NSFW and thus pornography (as it sometimes does with technology) has pushed SD performance even further; you can look to civitai with its huge collections of models (NSFW images are blurred but I would not suggest opening the site at work).