I used to commute on my folder since it folded up small for the Metro train I take for 11 miles each way each day. But then two things happened:
1. Los Angeles Metro made "bike cars" by taking out four sets of seats in some cars.
2. One morning my folder flatted (well, really, had a blow-out) as I rolled it down the driveway at the start of my commute.

So . . . I grabbed my road bike as "emergency" commuter but I liked it so much better than the folder, just for riding position mostly, that I've never gone back. In the morning I have no trouble getting my bike in a bike-car on the train, in the afternoon sometimes a bit of a hassle, but totally worth it.

My road bike is an old ('98) GT Edge, steel, with compact double in front and 11-26 in the back; nothing fancy at all, but fine for my relatively flat commute.

Rick / OCRR