Well, it's got to be a tough, knock down, drag out, durable, dependable bike that can carry heavy loads, stand up to heat, cold, dry, wet, road salt and getting knocked around every now and then. When you start riding your bike every day to get where you go, you don't have time to sit on the side of the road making repairs, you need to get where you need to go. Commuter bikes are not light weights and they're generally not pretty, they need bullet proof tires and a brooks saddle and fenders to protect you and the bike. They need wide range gearing that gives good accelleration and a reasonable top speed while having low gearing available for climbing while loaded. Steel is the material of chioce as far as I'm concerned, the above is based on 12,000 - 15,000 miles of commuting each year for a number of years.
But most bikes will get you to work once in a while.
Commute, it's good for the body and the soul, It's well worth the effort., It makes every day an adventure.