What is the best soil to plant an Angel Wings cactus in?

I had to look up the name as I've never called a cactus an "Angels wing". I see it is the white bunny ears, Opuntia microdasys alba. I just use any purchased cactus mix and add some extra perlite or pumice to make it drain really well. These grow quickly, so they will need to be re-potted fairly frequently. They're not really good houseplants unless you keep them trimmed down.

I agree about the soil, the size, and the relative difficulty as house plants. Try that as an experiment if you want, but provide the most light you possibly can indoors (ideally right next to an unobstructed south-facing window, in the Northern Hemisphere). You will be able to monitor the light by the shape of the pads. If they start to stretch then you need to dial up the exposure.

Also a warning that the spines on the plant, while quite ornamental, are actually kind of dangerous. Technically they're not spines but glochids, but same difference when you brush up the side of your hand against it and end up spending an hour taking a dozen of them out afterwards. (Try duct tape.) Keep your plant out of the way of traffic, especially kids and pets, but also adults, and I speak from experience to say it doesn't take much of a misstep for things to go badly wrong. My plant got banned from the patio for this reason, even though it was in the corner out of the way.

If you ever have to handle it (for example with regular repotting, which I would recommend as it grows, to the best of your ability) you need to use gloves and exercise the highest level of caution not to accidentally get yourself in the way of the spines.

The glochids are horrible. Be very careful! I've also had many accidental run-ins with them.

Thanks everyone! Regarding the recommended trimming - how is trimming best achieved?

To prune it, just take a pair of tongs and a clean knife, then hold the pad you want to trim off with the tongs and cut it off at the joint where it is joined to another pad.

Thanks! Here's a picture of mine when I first brought it home! I love it.

I'm glad to see the seller was considerate enough to include a caution about the glochids. These are very pretty plants, and I hope yours continues to grow well for you.

I went out of town for 11 days and left my plants in the hands of a friend, and upon my return, my cactus is looking a little floppy. It seemed as though so of the branches could handle the weight of all of their pads, so I trimmed as suggested in this thread and stuck the trimmed pads into the soil. But now I'm noticing that some of the pads are developing spots that look like scarring? Or is this just new growth coming in? Can anyone tell me?