It has varied. If I'm doing a lightweight/credit card tour on a road bike, then I'll ride my usual setup with SPD SL clipless pedals. If I'm going on a longer tour on one of my heavier-duty touring bikes, carrying panniers etc, I'll generally use Shimano Saint platforms. The studs in those pedals give plenty of retention if one isn't sprinting, there are likely to be periods during the day when I'm walking around off the bike, and it reduces by one pair the number of shoes I'm hauling around.
And you're just as efficient at touring speeds with platform pedals. Being clipped in is not about maximising efficiency, it's about keeping your feet on the pedals at high power outputs.