I haven't fell over using SPDs (mtb style), unclipping is just natural, foot in lower position, slide it out and down. Simples, don't even think about it. Had a couple of near misses where the bike leans the opposite way to how I expect and I need to quickly unclip the other foot, but have always saved at the last second.
For long distance rides (say over 40 or 50 miles) I still sometimes use flat pedals as I find them a bit more comfortable. As the balls of my feet can get a bit sore, probably happens due to the smaller nature of mtb cleats compared to road, and the small pedals I use without any supporting material around them like on touring pedals. Or I use flats if I know I've got a fair bit of walking to do, as even with my shoes with fairly recessed cleats they are still slippery and grind away on uneven surfaces.