Why not both? For any sufficiently complex app you will have some form of logging either way, and then you can further pinpoint the issue with a debugger. Also

Why not both? For any sufficiently complex app you will have some form of logging either way, and then you can further pinpoint the issue with a debugger. Also, debuggers can do live evaluation of expressions, or do stuff like conditional breakpoints, or they can just simply add additional logs themselves. They are a very powerful utility.