I am by no means a expert but have used both. I really much prefer the SPD because of the safety factor. No reaching down to snug up and instant release when instant release is needed. I also feel that they offer more positive power transmission but that is just me. Put another way, nothing on Earth would ever get me to put my feet into traps and rats again as long as I live. I use SPD mountain bike shoes with recessed cleats and love them. Just got a new set after wearing my other set out after thousands of miles of use riding and, sadly walking while carrying the bike, now and again.
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"98% of the bikes I buy are projects".