I find using roasting in the oven the most convenient way: it takes some time, but you only have to stir a couple of times, so it’s a very hand off way to get a delicious roasting. Also, it doesn’t need preheating and afterwards your oven will be ready to prepare any other baking goods. Roasting kuromame in a pan needs someone to be near the stovetop for quite a long time, but the roasting results are as good as when using the oven. Roasting in the microwave is my least favorite option because it may be tricky to find the exact time you need with your microwave. Also, the roasting is less even, with more beans remaining hard (not so bad for making tea, but not ideal if you want to eat them).