Celgene Corp. (NASDAQ: CELG) and Biogen Inc. (NASDAQ: BIIB) are both biotech industry titans, but for investors who can only add one of these two stocks to their portfolio, which is the better buy? Although Biogen has an intriguing Alzheimer’s disease moonshot advancing through R&D, various potential blockbusters lurking in Celgene’s pipeline are closer to commercialization.