My favorite handle material?
Overall, it would be micarta, G10 or FRN. It really depends upon the knife.
Normally, I try to avoid metal handles but, there are exceptions (SAK Alox, for example). Also, I have seen a couple of knives with lightening strike carbon fiber that I thought were pretty cool but, as a rule, I stay away from CF. Wood and leather handles are fine on some knives. Like I said, it really depends upon the knife.