One technique that some triathletes use for the swim is the two-beat kick. This refers to a rhythm where you kick just once for each stroke. As the right hand slides into the water, the left foot kicks; then as the left hand goes in, the right foot kicks. Because this technique involves less kicking, it is beneficial for long-distance triathlon to save your legs for the rest of your day. However, I have found that for me it is also more efficient, feels better, and I think I am as fast or faster, perhaps because it helps to keep me more streamlined. Indeed, it appears that some swimmers even use this kick in competition, so it clearly can be as fast or faster for others as well.
Here are a couple of videos if you are interested in trying it out.