Investors in biotech stocks Jazz Pharmaceuticals PLC (NASDAQ:JAZZ) and Medivation (NASDAQ:MDVN) must be smiling from ear to ear, as each of these companies has been a monster winner for long-term investors. In the past 5 years alone both of these companies have gone up more than 10 times in value, leaving a comparable investment in the S&P 500 in the dust.

MDVN Chart

We Fools like to invest in stocks with a strong history of market thumping returns, so we asked our team of Motley Fool contributors to share their opinions on which one of these two companies is the better buy today.

Todd Campbell: In my view, it's Medivation that is the more intriguing of these two stocks. 

Medivation already markets Xtandi, a prostate cancer drug that has become the market share leader in third line post-chemotherapy patients and is quickly becoming the go-to treatment in second line pre-chemotherapy patients, and it could soon deliver positive late stage trial results on a second cancer drug, talazoparib.
In August, Medivation forked over $410 million in cash upfront to land the rights to BMN-673, or talazoparib, a PARP inhibitor in late stage breast cancer trials. The ongoing phase 3 studies should read out data by the middle of 2016, and if those results show that talazoparib extends progression-free survival, then an FDA filing could come shortly thereafter. In small phase two studies, up to 72% of patients responded to treatment or had stable disease profiles when receiving talazoparib.
If talazoparib does pan out and eventually wins regulatory approval, it could become a significant drug for Medivation -- up to 10% of breast cancer patients possess a mutation to the BRCA gene that benefits most from this PARP inhibiting approach. According to the American Cancer Society, more than 220,000 cases of breast cancer are diagnosed every year, a rate implying that one in eight women will develop the disease at some point in her lifetime.

Since Medivation has already proven that it knows how to successfully commercialize a cancer drug -- Xtandi's nearly $500 million in Q2 sales were up more than 100% year-over-year -- and there's a significant unmet need for new therapies targeting breast cancer, I believe that Medivation is one of the most interesting biotech stocks out there for investors to consider owning in the coming year. 

Brian Feroldi: Medivation certainly looks like an interesting opportunity right now, but when forced to choose I think I'd give the slight edge to Jazz. Here's why.

Jazz has been growing like a weed thanks to Xyrem, the company's flagship narcolepsy medication. Sales of Xyrem grew 30% to nearly $250 million in the most recent quarter, making the drug a shoe-in to reach blockbuster status in 2016. Meanwhile, Xyrem is only currently being used by 12,475 patients, but 160,000 patients are believed to have narcolepsy in the U.S. alone. The drug holds patent protections that don't start to expire until at least 2019 as well.
Beyond Xyrem, the company's pipeline has several compounds in late stage clinical trials that should help extend its leadership position in sleep, and the company is already awaiting FDA priority approval of Defibotide, a potential treatment for vena-occlusive disease that is projected to have peak sales potential of around $400 million. Add in the potential revenue from sleep medication JZP-110 and the potential of a pediatric indication for Xyrem, and Jazz could have years of strong growth ahead of it.

Source: Jazz Pharmaceuticals

Like most other biotechnology stocks, Jazz's share price has collapsed this year, and is currently down more than 38% off its summer highs. For the full year, Jazz expects its non-GAAP earnings per share to fall to between $9.45 to $9.75, meaning its shares are currently trading for a measly 12 times 2015 earnings estimates. Extend that number out to 2016 earnings estimates and its price-to-earnings ratio drops all the way down to 10. Considering the company's solid pipeline and history of executing, I'd say that's a steal.
I'll admit that Medivation offers investors the possibility of stronger, faster growth, but the value investor in me thinks that the smarter choice is Jazz right now. Of course, there is no rule stating that you can't put both of these potential winners in your portfolio.