Two sided (MTB) SPD pedals are a no brainer to get into with just a little practice, hence good for city riding and, off course, mountain biking. I also use them on all my bikes in winter, because the MTB shoes are a lot warmer besides being gentler on the underside of my neoprene over-booties. Once I don't need the booties anymore I switch most bikes over to the classic Look/Delta pedals, since the shoes are so much lighter, cooler and seems to transfer power just a bit more efficiently.

For really long rides (200k+), I still prefer MTB shoes for prolonged comfort

One sided (road) SPD pedals makes no sense to me.