I've commuted using both the Shimano A530 platform/SPD and the Shimano M540 double-sided SPD>

While I didn't think the A530's were that bad, I like the M540's a LOT more. If you do hit the platform side of the A530's you can just keep pedaling and then switch to the SPD side once you are going comfortably fast. My reason for switching back to the M540's is that I almost never used the platform side of the A530's. Maybe once a month I would ride my bike 4 blocks to grab lunch during the day at work. I could have just as easily put on my SPD shoes for that. The M540's are great because I can just mash my foot down and be clipped in without even thinking about it. Unless you plan to ride in street shoes often, get the M540's.