It looks like a combination of algorithm and staff picks. I've studied the list and determined it has to do with traffic surges (HP or organic), if it's newly published, QAP score, and the rate at which all hubs in sub-topic categories are published and compared to each other, i.e., the competition factor. I think that's why they bounce around so erratically from one position to another. For example, say today I do a hub about apples with 3 images, a chart on how to use different types, and 2 ad capsules. And tomorrow you do a hub about apples with 10 images, a chart, a poll, a video, and 4 ad capsules. When our hubs are on the featured list, yours will likely be ahead of mine on the All Topics list, as well as the sub-topic list about fruit.