Another vote for SPD. For the road, I like the Shimano A520 and A600 pedals. I think they give better support than the double sided mtb pedals. I also prefer the single release cleats as I imagine(?) they may be more predictable. A quick twitch of the heel and you are unclipped. Same motion, same result every time, muscle memory. Earlier this year I bought some SPD-SLs and 3 bolt shoes, just because. I gave them a good try for several months but couldn't get comfortable. The engagement didn't seem as positive as SPDs and they offered no more support than my Axxx pedals. The left cleat was already worn out when I gave up on them, just from putting a foot down at stops. On the other hand, the 3 bolt SPD=SL/Look types do seem much more popular among road riders.