This year might have started off poorly for biotech stocks, but things have certainly changed after the surprising election results. Two of the biggest biotechs around, Biogen (BIIB 4.56%) and Celgene (CELG), are now enjoying nice runs. Which of these two stocks is the better buy for long-term investors? Let's see how Biogen and Celgene compare.

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The case for buying Biogen

Biogen's revenue growth isn't exactly awe-inspiring. The biotech's multiple sclerosis franchise saw mixed results in the third quarter. While Tecfidera's sales increased by 10% compared to the prior-year period, those gains were wiped out by declining sales for Avonex. Tysabri made the difference, with 7% year-over-year sales growth.

However, there are several things on the way that could make Biogen a smart investing pick. The company plans to spin off its hemophilia drug business into a new company, Bioverativ, in early 2017. Sales for hemophilia drugs Eloctate and Alprolix are soaring. Spinning off the new company should unlock some value for Biogen shareholders.

Spinraza (nusinersen) should also be a success story. Biogen and partner Ionis announced great results from late-stage studies of the experimental drug in treating spinal muscular atrophy. Biogen hopes to win regulatory approval in the U.S. and Europe. A U.S. launch of Spinraza could come as early as late 2016, if the drug gains approval. Spinraza could reach peak annual sales of $1.7 billion.

Biogen also has high hopes for aducanumab, its late-stage candidate for treating Alzheimer's disease. The U.S. Food and Drug Administration recently granted fast-track designation for the drug, which could lead to speedier approval if all goes well in clinical testing.

What about Biogen's leadership position in multiple sclerosis? Zinbryta could help improve sales somewhat, although the drug might also take sales away from Avonex. Biogen could also receive significant royalties assuming Roche wins approval for Ocrevus.   

The case for choosing Celgene

Celgene, on the other hand, isn't having any problems in growing revenue. Total sales in the third quarter jumped 28% year over year. Blood cancer drug Revlimid continues to be the top performer for Celgene -- and continues to keep the solid momentum going.

The other major products in Celgene's lineup are also doing well. Sales are strong for multiple myeoloma drug Pomalyst and Otezla, which treats plaque psoriasis and psoriatic arthritis. Cancer drug Abraxane isn't generating significant sales growth but should still pull in close to $1 billion this year.

Another blockbuster could be on the way. Celgene picked up ozanimod with its 2015 acquisition of Receptos. The drug is in a late-stage study for treating multiple sclerosis. A late-stage trial is also underway for ozanimod in treating ulcerative colitis. Celgene thinks ozanimod could reach peak annual sales between $4 billion and $6 billion.

Celgene's pipeline includes an additional late-stage candidate that could be successful. The phase 3 study for oral GED-0301 (mongersen) in treating Crohn's disease is enrolling patients. Data from the study is expected in 2018. The experimental drug could bring in over $3 billion in peak annual sales if ultimately approved.

With its current products rocking along and potential new drugs on the horizon, Celgene thinks it can grow earnings at an annual rate of 23% through 2020. Wall Street analysts are only slightly less optimistic, projecting annual sales growth of just over 22% during the next five years. 

Better buy

This decision is easy, in my opinion. Celgene is the better buy for long-term investors.

Biogen does have plenty to like, especially with Spinraza. I hope that Biogen also succeeds with aducanumab, but Alzheimer's disease has proven to be a tough indication to treat so far. On the other hand, Biogen's lead position in multiple sclerosis could be in jeopardy from rivals in the future (including Celgene's ozanimod).

Meanwhile, Celgene is firing on all cylinders and has tremendous opportunities for growth. There's no sure thing with investing in stocks, but Celgene might be as close as you can get.