[yekim]

Depends on what you're debugging.

Desktop apps w/ C/C++ -- IDE based debugger (Visual Studio, GDB w/ a front end, ADB) print / logging statements

Embedded C -- IDE Debugger (Green Hills, ARM DS-5, IAR, Eclipse w/ remote GDB, etc) GPIO ports, logic analyzers, oscilloscopes, etc)

Apps -- ADT / ADB, print / logging statements

Python, bash, sh, .bat scripts -- print / logging statements

As many others have mentioned, having a consistent bug reproduction methodology is vital, a strong mental model of the SW and its various components is important, and a willingness to dive deep and question assumptions is critical. Ie don't always expect your compilers or various OSes to be infallible.