I'm responding to my own thread... but oh well...
My main commuter is a Surly Long Haul Trucker. My commute is 39-miles round trip. I used to commute on a lightweight road bike, but I had to carry my stuff in a backpack and that got old quick. I tried a rear rack on the road bike, and it flexed a lot when pedaling out of the saddle... there was just no way I could live with that. The Surly is everything I want in a commuter. It's tough, takes wide tires, hauls heavy loads, and has all the braze ons that I need.
For my "city bike", I have two old fixed gear conversions. One has fenders and 27X1 1/4 tires, and the other is sort of a "go fast" fixie with narrow 23c tires and no fenders.
My MTB is an old Trek (I think model 800). I'm going to try it soon, when we get some snow.