It might not be obvious to the casual observer, but right now, today, Amgen (NASDAQ: AMGN) stock offers one of the best values available in biotech. Why?

Three reasons.

1. Amgen is cheap
When you stack up Amgen against a couple of its bigger rivals -- Johnson & Johnson (NYSE: JNJ) and Novartis (NYSE: NVS), it's clear that Amgen stock is the best bargain of the three. Its 16.5 price-to-earnings ratio is 10% cheaper than Novartis's 18.3, and offers a near-28% discount to the 23 P/E at Johnson & Johnson.

Amgen also offers a cheaper "forward" P/E ratio -- just 11.8 -- and costs a mere fraction of the valuation on its rivals when measured under the rubric of price-to-free cash flow. Costing a relative pittance of just 18 times free cash, Amgen's valuation is cheaper-by-half than the P/FCF ratios at either Novartis or J&J.

2. Amgen has the best record around
Over the past five years, Amgen has grown its annual profits more than twice as fast as its closest rival. Amgen's notched a 15% annualized earnings growth to Novartis' 6.8%, and blown Johnson & Johnson's anemic 1.2% growth rate completely out of the water.

And if Amgen stock looks great in the rearview mirror, it looks nearly as good when viewed through the windshield. Going forward, Amgen promises to maintain its lead. Analysts on average see the stock outgrowing J&J by nearly half, and eclipsing Novartis's growth rate by an even larger margin.

3. Amgen pays you best
Perhaps most important to investors, though, is the fact that out of the three biotech stocks discussed above, Amgen is the firm generating the most cash from its business, giving you the biggest free cash flow bang for your investing buck.

Measured by dividing a firm's market capitalization (the price you pay for Amgen stock) into its free cash flow (the money your investment generates for you), Amgen offers investors quite simply the best "free cash flow yield" of the three firms named. Put even more simply, for every $1 you invest in a share of Amgen stock today, you can expect the firm to generate 6.8 cents worth of real, cash profits on your investment. What's more, Amgen has outperformed its rivals in this regard pretty consistently over time.

AMGN Free Cash Flow Yield Chart

AMGN Free Cash Flow Yield data by YCharts.

Amgen may ultimately use this cash to pay you bigger dividends (its current yield of 1.9% does, after all, lag both its rivals'). Or Amgen could use its cash to buy back shares (increasing the size of your stake in the company for every share it takes off the table), or to reinvest in its business and maintain its stellar pace of growth. Any way you look at it, though, Amgen's ability to generate cash offers investors a great reason to invest.

And that, Fools, is the reason I think now's a great time to buy Amgen stock.

Fool contributor Rich Smith has no position in any stocks mentioned. The Motley Fool recommends Johnson & Johnson. The Motley Fool owns shares of Johnson & Johnson. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.