I've been running double sided SPD pedals for the last year or two and really like them. I think one can do slightly more adjustment for road pedals (wedges?) But, that hasn't been an issue for me.

I thought I'd try single sided SPDs (2-bolt) for my latest build. And they seem to be designed to always hang upside-down, so getting started means flipping the pedal, and hopefully clicking in. And, of course, I decided to try these just a couple days before some wicked hill climb rides. The pedals look sleek, but I should have stuck with the standard double-sided pedals. Missing a click on a 20% slope can be pretty unforgiving.