MBSR:
As has been suggested, it is the MAKER and DESIGN of a single trigger that makes it reliable -- or not. The issue then becomes: what brand of SxS are you considering? If not English or the best Italian, then I'd personally opt for the double trigger. Absolutely reliable. Absolutely selectable. And absolutely as fast as a single with a bit of practice. In my humble experience, there is no comparison. But suit yourself.

Best, Kensal