proper arm form for freestyle?

Hi, My swimming interest lies in triathlons, and I have heard of two fairly different techniques for freestyle. I've been getting swimming tips from active.com. They advocate hand entering the water thumb & forefinger first, rotating to flat, and then the arm traces an "s" shape under water, elbow slightly bent. Recently, I was told by a master's coach that the proper form is to have your hand enter the water finger tips first, then bring the arm through the stroke with the elbow at 90 degree bend so the arm below the elbow is parallel to the bottom of the pool. I've tried both, and the second way seems more awkward (probably because it's new to me), but the only other difference I can find is that it seems to use different arm & back muscles. What's the "right" form and why? Thanks, tri'ing