Originally Posted by zoridog
I think the best commuter is the reliable bike that you aren't in love with. You're going to expose it to thieves, heavy mileage and the elements. Don't bring your main ride.
+1. I'd vote Al for the cheapness, lightness and resistance to damage from the elements. My primary commuter is steel, and I can't imagine riding that thing for more than 10 km at a time. I have a secure lockup at work, so I will eventually ride my new CF bike downtown. It's so freaking comfy. I also plan to build up an easy-riding steel SS/FG this spring, which I hope will be more pleasant than my current ride.