My opinion:

Touring bike with 700x25 or 28 tires (depending on roads), fenders, rear rack with panniers and rain covers if needed. I guess it depends on how far you have to ride, but if more than 15 miles or so round trip, I would go with a touring bike or cyclocross bike over a mtb with slicks.

Reliable deraillers, shifters, and brakes (LX or XT). High-spoke count wheels. Tires should be Armadillos or something similar, with thick tubes or Mr. Tuffy's.