You can get shoes compatible with both, but I don't really get on with my pair and I'm not sure whether that's me or the shoes.
For touring, audax (i.e. long days riding, quick but not racing) and commuting I have a strong preference for my walkable shoes, that go with SPDs. They're much more suited to when you have to get off at a stop or if a hill becomes too much. In stop-start riding it's much easier to get a couple of pedal strokes in before clipping in, or ride very slowly unclipped in traffic, if you're using shoes with a conventional sole (which means touring or mountain shoes) and a suitable pedal. True road shoes slide off the pedals if you try that (or at least mine do). If you're thinning of a lot of winter riding, there's much more choice of winter bike footwear in SPD (and sandals for that matter)
For SPDs you can also get cleats that release if you pull up hard, but I've never tried them. This is the one hardware factor that may actually make a difference.
The actual ease of unclipping, once you're used to the movement, and assuming no trouble with your legs isn't a big factor. I have my SPDs set quite loose because that's what I've always done, but I recently did a track session with Look Keos (more like SPD-SL) and while noticeably stiffer to twist out of, the actual twisting action was no more difficult (doing it on fixed gears was). It all comes down to practice, so get plenty while leaning on something solid.