Adding up to my previous question, what clef was first and why? I guess there should be answers somewhere out there but I can't find them.
According to both the Harvard Dictionary of Music and the Grove Encyclopedia, the first clefs to be used in a manner anything like the modern usage are F and C clefs. The vast majority of early plainchant manuscripts use these. Even earlier, Guido d'Arezzo would use colored lines in his staves to show notes--a red line for F and a yellow line for C--which seems to further cement the idea that indicating F and/or C was seen as most useful initially. Grove suggests that this is probably because those two notes are especially common in the vast majority of plainchant, which certainly makes sense to me.
EDIT TO ADD: I realized that for people not as familiar with clefs, a bit more clarification might be helpful. The modern bass clef is a descendant of the F clef used in plainchant notation. The modern alto and tenor clefs (the former used only for viola, the latter used occasionally for cello, trombone and bassoon) are descendants of the C clef.