Phoenix for me. I've only tried Phoenix, RealFlight G3.5, and FMS. For me, accurate heli physics is the absolute top priority, along with the ability to edit aircraft settings to get them to behave as closely as possible to my real aircraft. I don't care much at all about other features such as aircraft break-up animation on crashes, cockpit view, online-multiplayer, or the ability to create new aircraft skins. So for me Phoenix wins out even though it doesn't have many of the features that G3.5 has, because I think the helis behave more realistically.