Flat. Pinned Platforms FTW
I had SPD on everything, but when the shoes got tatty and I was looking around at how to replace them, I threw in the towel. I'm doing great with ~$25 Wellgo MG-1/MG-3 pedals off eBay that will probably never have to be replaced and ratty old tennis shoes from salvation army, happily knowing I"ll never have to drop ~$100 on a pair of SPD shoes every couple years.
The only thing I miss about SPD is sometimes on my hardtail, rocks can bounce me around/off the pedals, but with practice it's happening less, and I've never crashed because of it -- which I cannot say about SPDs, I've had a good half-dozen skinned knees because of not being able to unclip in time.