You could buy these in any month, really.The stock market has performed relatively well since the beginning of the year although, of course, there is no guarantee that it will maintain that momentum. Who knows what curve ball the future has in store for us? Regardless of what happens, investing in market leaders with robust underlying businesses and excellent prospects is still usually a good idea.Let's consider two such stocks in the biotech industry: Vertex Pharmaceuticals (VRTX 1.36%) and Regeneron Pharm ...