Several big biotech stocks have proven to be big winners for investors in recent years. Celgene (CELG) and Amgen (AMGN 0.04%) definitely belong in that category. In the last five years, Celgene's share price has more than tripled, while Amgen stock is up over 140%.

But which of these biotech stocks is the better buy for investors now? Here's how Celgene and Amgen compare.

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The case for Celgene

Why buy Celgene stock? It's simple: growth. Both the company and Wall Street expect average annual earnings growth of 22% over the next several years. You're not going to find many large-cap stocks that can claim that kind of growth potential.

Celgene should get plenty of help from current products. The company's top-selling drug, Revlimid, made nearly $7 billion in 2016, a 20% increase from the prior year. Sales for another blood cancer drug, Pomalyst, grew even faster. Celgene reported 2016 sales for Pomalyst totaling $1.3 billion -- up 33% year over year. The real star in the biotech's current lineup, though, is Otezla. Sales for the psoriasis and psoriatic arthritis drug soared more than 115% in 2016 to just over $1 billion. 

While Celgene should continue to enjoy higher sales for each of these drugs, the company's pipeline should be the biggest driver of growth over the next few years. Celgene hopes to receive approval for four new drugs by 2022 that could all generate annual sales of more than $2 billion and another six drugs that could generate annual sales of $1 billion or more. 

Ozanimod should be the first of the biotech's potential blockbuster drugs to reach the market if all goes well. Celgene announced positive results from a late-stage study of ozanimod in treating multiple sclerosis in February. Ozanimod is also being evaluated in another late-stage study for treatment of ulcerative colitis. 

Are there any downsides for Celgene? Sales for its pancreatic cancer drug Abraxane didn't grow very much in 2016. It would be a stretch to call that a downside, though, since Abraxane still made nearly $1 billion. There's always the possibility that Celgene could experience pipeline setbacks, but that's a risk with any biotech. Overall, Celgene appears to have plenty of huge positives with few identifiable negatives.

The case for Amgen

Amgen lays claim to three blockbuster products with double-digit percentage sales growth in 2016. Sales for autoimmune disease drug Enbrel increased 11% to nearly $6 billion last year. Sensipar, which treats secondary hyperparathyroidism (HPT) in chronic kidney disease (CKD) patients, saw a 12% jump in revenue to nearly $1.6 billion. Sales for osteoporosis drug Prolia soared 25% to just over $1.6 billion. 

Another drug could be Amgen's big winner for the future. PCSK9 inhibitor Repatha won approval for treating high cholesterol in 2015. Sales haven't taken off for Repatha, though, as payers restricted reimbursement for the high-priced drug. Amgen is hoping that positive results from a cardiovascular outcomes study for Repatha combined with its willingness to enter into contracts that refund the cost of the drug for any patients who have a heart attack or stroke will encourage payers to remove their access barriers.  

Amgen's pipeline includes 12 late-stage clinical studies. Several of those are evaluating the company's already-approved products in treating additional indications. One promising new late-stage candidate is experimental migraine drug erenumab. Amgen expects to submit for regulatory approval of the drug in the second quarter of 2017.

No biotech is in as solid of a position to beef up its pipeline through acquisitions as Amgen is. The company reported $38.1 billion in cash, cash equivalents, and marketable securities at the end of 2016. Amgen CEO Robert Bradway has hinted that the company could pursue big or small buyout opportunities. 

Amgen will need to do something. Several of its top-selling drugs face biosimilar competition that seems likely to intensify in coming years. 

Better buy

Which of these two big biotechs is the better choice for investors? I think the hands-down winner is Celgene.

Amgen should be able to use its cash stockpile to improve its prospects, but Celgene's future appears bright even without making any acquisitions. Investors wanting to buy a biotech stock with solid growth potential would be hard-pressed to find a better option than Celgene.