Currently using SPD. Haven't tried the rest yet. The reason I get SPD is simply it is commonly available everywhere and you can get replacement parts easily. 

Speedplay Zeros!

And you can use the special Keep on Kovers for Speedplay Zeros while you are on the bike. Protect the cleats even further.

Downside?
1) Need regular maintenace on the pedals & cleats
2) Need to grease them using a grease gun

But these are simple maintenance steps and does not take more than 30 mins.

I chose SPDs for the dual-sided operation and walkability.
Chose the multi-release SH-56 cleats for ease of unclipping when I was a noob. So far (touch wood) no falls when coming to a stop :)

Speedplay, push down to clip in. Need some getting used to the clipping in method as it is different from the rest. Once it get the hang of it, it is fuss free. Unlike typical clipless where the cleat is on the sole of the shoe, speedplay's cleat is the pedal and the clipin mechanism is on the sole of the shoes. Free float is adjustment via the side screws.

Pros
1) durable, almost maintenance free
2) no need to replace the cleat (pedal) some riders have 30,000 miles on them and still using them.

Cons
1) New ones need abit of running in.
2) higher learning curve?