Biotechnology stocks are notorious for roller-coaster like highs and lows, but that doesn't mean that every biotech that heads lower will climb again. Figuring out which companies are bargains and which aren't can be particularly tough in this industry, so we asked three of our top analysts to pick one biotech company that they wouldn't buy and tell us why. Read below to see what they think are the riskiest plays in the industry.

George Budwell: I'll jump in first and get this started because it's not hard to find a lot I don't like about Arena Pharmaceuticals (NASDAQ:ARNA). Their shares have nosedived by 30% this year due to the flagging commercial performance of its fat-fighting pill Belviq (lorcaserin). Despite this massive discount from its former highs, I still wouldn't buy shares anytime soon. Perhaps what sums up my pessimistic view the best is the stock's present valuation. Namely, Arena shares are trading at roughly 30 times 12-month trailing revenue, meaning that investors are probably pricing in potential label expansions for lorcaserin or a vastly improved commercial performance for its current indication, chronic obesity.

The first problem is that a label expansion is at least two years away. Next, the drug is set to face greater competition on the obesity front due to the recent approval of Contrave and the likely approval of liraglutide. Overall, I don't see enough in the way of top-line growth to justify this lofty valuation and it's too early, in my opinion, to bake in label expansion revenue.

Seth Robey: Interesting point George, but in my eyes it's Aegerion (NASDAQ:AEGR) that doesn't quite fit the bill of a Foolish long-term investment, even after falling precipitously from its 2013 highs.

Aegerion markets Juxtapid, a MTP inhibitor approved to reduce the bad LDL cholesterol in patients with homozygous familial hypercholesterolemia, or HoFH. As one of the only treatment options for HoFH patients, who require more intensive therapy than traditional cholesterol-lowering drugs, management priced Juxtapid at a stunning $295,000 per year.

However, a slower than expected launch has forced cuts to revenue guidance and an emerging class of drugs could supplant Juxtapid's standing. PCSK9 inhibitors from Amgen and the perennial duo of Regeneron and Sanofi have shown stellar results in a number of lipidemia indications, including HoFH. In fact, Juxtapid's 40% reduction in LDL in HoFH patients is only slightly better than Amgen's 31% reduction with evolocumab. Not to mention, Juxtapid's price tag also comes with a risk of liver toxicity. With slow sales supporting a $1 billion market cap, emerging competition, and lack of secondary growth drivers, I can't get behind an investment in Aegerion.Juxtapid label and data: 

Todd Campbell: Anyone who has followed the biotech industry for a while can tell you at least one horror 'pop-and-drop' story. But amid all the scary stocks in the industry, the one name that I wouldn't buy is Dendreon (OTC:DNDNQ) -- one of biotech's biggest lightning rod stocks.

I'm not saying that Dendreon's Provenge wasn't a breakthrough. And I'm not arguing that Provenge hasn't made a big impact on prostate cancer patients. But I do think that Provenge's launch and subsequent management has probably been one of biotechs biggest disasters.

Few drugs (outside of the diet drugs, right George?) have been as over-hyped as Provenge. As a result, the bar was set so high that Provenge didn't' stand a chance. The company over-invested and spent far beyond Provenge's potential, significantly debilitating the company's balance sheet and driving its debt to asset ratio north of 150%. Despite a significant restructuring, Dendreon's cash continues to drop and with rising competition from other prostate cancer drugs eating away at market share, Dendreon's survival is just too big a gamble for me to risk.