If you're recording on a very high quality Metal Bias cassette (also known as Type IV), Dolby C is the way to go. You will have absolutely no background noise what so ever unless you listen very closely on headphones during silent places and the recording will sound nearly identical to the source...almost like a FLAC or WAV file with minimal frequency loss.
But keep in mind, if recording in C, it will always need to be played back on a deck with C. Otherwise it will sound compressed playing back with B.
If you're recording on a Chrome cassette (also known as Type II), Dolby B as you had it is the way to go as the C can make things muddy since you don't have the high range that Metal offers. If recording on a Normal bias (Type I), do not use any dolby cause it will be very muffled.