Big biotech stocks have been on a roll lately, and industry mainstays Celgene (CELG) and Gilead Sciences (GILD -1.74%) are no exceptions. Each stock has gained more than 50% over the past year as these two companies surge behind older established cash cow drugs while putting their hopes behind ballyhooed new therapies in development and on the market. In the long run, however, which biotech stocks are poised to reward investors the most?

Celgene has a lot going for it. The company's flagship therapy, Revlimid, saw revenue jump more than 13% year over year in its most recent quarter. However, while Revlimid's patent won't expire for some time now, Celgene's reliance on the drug -- Revlimid makes up more than 60% of the company's total sales -- has led to some questioning the stock's long-term future. Gilead, on the other hand, has investors excited behind up-and-coming HIV therapy Stribild and recently approved oral hepatitis C drug Sovaldi, which has exploded onto the scene in its first few months on the market.

Can Sovaldi's promise power Gilead's future, or is Celgene and Revlimid's reliability the best bet for your portfolio? Find out in the video below as Motley Fool contributor Dan Carroll takes you through what makes these two big biotech stocks so appealing -- and which one is the better buy for your financial future.