A moka pot is kinda special. If you want something a bit stronger than normal drip coffee, it delivers quite easily.
It can also blow burning hot steam through the grinds unless you know what you’re doing, which results in bitter coffee. Hoffman made a great video about that, so be sure to check it out. If all you want is convenience, get the cheapest coffee you can find and let the steam do its thing. Use plenty of milk to cover the flaws of both the method and the beans. With milky drinks, the coffee doesn’t really matter. The milk does the heavy lifting, as long as it has enough fat.
If you want to make good coffee with a moka pot, watch the Hoff video and grab the cheapest light roast you can find. It doesn’t have to be specialty coffee, as long as it’s light. In my area, every supermarket carries at most 2 light roasts at very reasonable prices due to the massive production volume. The rest of the aisle is occupied by approximately 40 medium roasts and 20 dark roasts, which I ignore entirely. They don’t taste that great even though they cost more.
You’ll need to put some time, effort and skill into the brewing technique, but you can make something quite tasty. Due to the dimensions of the pot, the result is always going to be strong. Don’t expect anything close to drip coffee. With a light roast, you can drink it as is. I’d recommend tasting it before adding any milk.
You can also cut the brewing short halfway, which produces something closer to espresso, but without the fine grind and high pressure. Honestly, I couldn’t tell the difference when I tried it with Lavazza Espresso beans. Apparently that’s where I bump into the limitations of my tasting skills.
One thing you shouldn’t do: don’t put your fancy light-roasted specialty beans in a moka pot. Pour over and AeroPress will produce something far more delightful. Could be a skill issue, but I’ve never been able to make the most of expensive beans in an espresso machine or a moka pot.
With espresso and moka pots, always go with something on the cheaper end of the spectrum. Check what’s available in your area, look at all the lightest options, sort by price, and pick the cheapest. Ignore all medium and dark beans for now.