I have a lot of them and my favorites are usually the weight swap ones. Tservo96 has some of the most descriptive and detailed swapping I've seen with "The Lab" being one of my favorites from them. I also really like all of the old Izlude13 weight swap stories. There are also a few stories by kuzumochi on pixiv with some of the best dark weight swap i've seen, but they don't have an official english translation.