Egg beaters, mx version or whatever the cheapest ones you can find are.
They don't clog up, and I've ridden them in street shoes, not a biggie. It's a mental thing about the size of them. And release requires lower effort than on road pedals. My Ultegra's with the tension backed off completely required a lot more effort to get out of than the egg beaters.
I broke my ankle last winter and in the spring, I needed to assist my left foot out of the Ultegra's but could manage to clip out without the having to pull my heel with my hand when I was on my mountain bike.