My best commuter was a folding Dahon Helios I used in San Francisco. Jay Gaerlan, a gifted bike guy in San Francisco, (http://www.gaerlan.com/)used
the Helios aluminum frame and added front suspension, seat post suspension, 24 gears, fenders, a rear rack that allowed me to carry a briefcase pannier or a grocery sack pannier without hitting my heels or the ground, and combo SPD and platform pedals as well. He chose Vuelta rims that never went out of true, and Schwalbe Marathon tires that never suffered a puncture despite daily rides through SF streets with debris and potholes.
The big advantage of the folder in SF was being able to take it on the BART subway trains, folded, at any time of the day. Ordinary bikes are restricted to the first and last cars, and forbidden during rush hours. Busses and the CalTrain communter train allow bikes all the time in special facilities, so folding was not an advantage there, but being able to take the bike into a restaurant or hotel or library, folded, was a huge advantage. I had a hybrid stolen, while locked with a Kryptonite cable lock to a standpipe in a lighted, covered garage patrolled by an off duty SF policeman at an in-town SF hotel. The cable had been cut and no one saw anything. After that, the folder came in with me when I was visiting in town. Most places simply accomodated it as they would a wheel chair (which the folded bike sort of resembles). Great commuter -- carried my gear to work and back, and on errands. Quick to set up and take down, every bit as fast as the public transit in SF, but with a reliable schedule: I could leave when I wanted and be on time at the destination.
San Francisco bound