Cost and availability. That's what finally decided it for me. The independent shop where I get most of my service work done (I have too many irons in the fire right now to do it myself) hooked me up with a supplier located about five blocks over from where I usually buy my other parts and filters. They also happen to sell the correct Mann filter for a dollar and some LESS than what I can buy the same Wix unit.

Thanks to all who took the time to respond and apologies to anyone who may have gotten offended. I've damn near worn out my keyboard searching this forum alone.