Not having commuted yet, my opinion has little weight behind it, but i have thought about it a lot.

For me, my commute will be 28-40 miles per day depending on the route and wether or not I use the train for a portion of the route.

So, I would say requirements will vary depending on the mileage. One with a 5-10 mile round trip has much different requirements from one with a 30+ mile round trip. efficiency is far more important on a longer journey i'd say.

take care,

Jester