I use double-sided spd pedals with a flat pedal on the other side. Best of both worlds. since going from plain flats to these, I definitely feel safer and more in control when clipped in.

Being able to put down a foot quickly will not help you much in a high speed crash, only a low-speed one. I fell over one time when first learning how to use my new pedals...since then, it's been almost second nature.

SO MY SUMMARY:

1. So, for regular riding and worries about crashes at speed, I'd say clipped in Is safer because it gives most control without feet slipping from the pedals.

2. If you are practicing your track-stands, and are worried about falling over, then flat pedals are safer.

3. I can't imagine using old-fashioned straps. That's scary to me.