The phrase 'investment piece' gets bandied around too often, but a classic watch is truly deserving of the title. Part of the Chopard's signature 'Happy Sport' collection that was first created in 1993, this 18-karat rose gold and stainless steel timepiece is encased with five free-moving diamonds that glisten as they float across the silver-toned guilloché dial - a concept originally inspired by the dancing droplets of a waterfall. It has beautiful curved edges and links that sit…