I ride about 2500 miles per year, mostly road.
At one time, I used SPDs (Shimano SH-51), but I got knee pain from a misaligned cleat. In addition, I prefer to ride with my feet slightly pronated (heels in, toes out, like a duck), so I felt like I wanted more float from my cleats. SPD cleats offer around 5 degrees of float. Too, the shoes I had for SPDs were not stiff enough in the sole, so I was getting hot spots on longer rides. After 40-50 miles I couldn't wait to get off the bike.
I switched to Speedplay Zeros about 4000 miles ago, and I've been very satisfied. They offer a huge amount of float relative to SPDs (15 degrees, about three times as much). The cleats for Speedplays are not cheap ($40 vs. $20 for SPDs), and they do wear, but you can fight the wear to a certain extent with covers (http://www.keeponkovers.com/Product.html). The Speedplay cleats need to be lubed-- I use Pedro's Ice Wax-- and as a result they do pick up dirt, which, if you are careless, can make it harder to clip in.
I know riders who do three times the mileage that I ride, and they're good with SPDs.
Bottom line, all of the contact point stuff-- bars, saddle, shoes, pedals-- are a personal matter, and to a certain extent you need to find what works for you. The bars, saddle, shoes, and pedals that work for me may not be so good for you.