Originally Posted by
tinrobot
SPDs are more useful because you can actually walk in the shoes. If you ride over 40 miles, however, the small cleats will press against the bottom of your foot creating a hot spot. That's the point where SPD-SLs work better.
This is really only an issue if you buy crappy shoes. I use Crank Brothers Eggbeater pedals on both my commute and road bikes. For road riding, I use Shimano SH-M160 shoes. They have a stiff enough sole that I don't notice any hot spots due to the smaller Eggbeater cleats...