Hereof, what is the best format for headphones?
A lossless audio file format is the best format for sound quality. These include FLAC, WAV, or AIFF. These types of files are considered “hi-res” because they are better or equal to CD-quality. The tradeoff is that these files will be very large.
Additionally, what is the best default format for audio? I see that Windows sets the default output format at 16-bit, 44100 Hz (CD Quality). Most of my music is in this format, but most of my movies use a 16-bit at 48 KHz format (named DVD quality in the Sound panel). The Windows system sounds are 16-bit at 22050 Hz, which seem to fit nice and evenly into 44.1 KHz.
Keeping this in consideration, what format should I use for my mic?
44.1/24bit is plenty for most applications. Unless your doing audio for SACD (96K/24bit) or DVD live show (48/24bit), and the music is well recorded jazz or classical, there really is no need to do anything beyond 44.1/24.
What should my microphone default format be?
By default, it's set to 1 channel, 16 bit and 44100 Hz, which is CD quality. There are many other options, including DVD quality, which you can use if you have a high-quality microphone. If you go back to the Recording tab, select Microphone and click on Configure, the Speech Recognition dialog will appear.