Buy high and hold forever? Maybe that's the best course of action when it comes to fast-growing, high-quality companies. Not every stock that hits new highs will continue to generate market-beating returns, but best-in-breed companies could continue their winning ways. Our investors think Weight Watchers (NYSE: WTW), Shopify (NYSE: SHOP), and Align Technology (NASDAQ: ALGN) could still see their share prices climb, despite recently doubling.Rich Duprey (Weight Watchers): Weight-loss specialist Weight Watchers hit gold when Oprah Winfrey signed on as an investor two years ago.