It depends on how big you want your webcam video to be. If you are planning to show yourself in a small corner of a screen like most software instructors do (and the rest of the screen to be for instance PowerPoint or a screen recording), then any webcam will do, even the one that comes in a standard $500 laptop. You see, when you squeeze an image, you squeeze out the detail anyway. But if you want to really show yourself in the whole screen, then I wouldn't even use a webcam. Use a mirrorless camera and use it as a de facto webcam. The image is 1000 times better than the best webcam because you get true depth of field, whereas with webcams, it's either fake depth of field or no depth of field whatsoever.