As 2013 draws to a close, investors have their attention fixed on which companies stand out heading into the new year. It's been a fantastic year for many health care stocks, including GlaxoSmithKline (GSK -0.92%), Johnson & Johnson (JNJ -0.69%), and Pfizer (PFE -0.19%), which have all performed extremely well.

Of course, the question is whether this positive momentum can continue into next year. The broader market has registered impressive gains, meaning it may be a good time for you to curb your enthusiasm for 2014. That's why, in light of GlaxoSmithKline's and J&J's diversified business models, you may want to favor those two, and by the same token, take a cautious approach to Pfizer.

Why caution might be warranted in 2014
The S&P 500 is up a superb 25% as we near the end of the year. So it's only reasonable for you to get a little defensive with your portfolio. That's where health care heavy-weights GlaxoSmithKline and Johnson & Johnson stand out. They both operate highly diversified businesses in many areas of health care, including segments that can provide steady profits, should the broader economy turn south.

GlaxoSmithKline operates in three segments, pharmaceuticals, vaccines, and consumer health care. Pharmaceuticals comprise the bulk of the company's earnings, but vaccines and consumer health together represent a quarter of its operating profit. These two segments are usually less volatile than pharmaceuticals, as they're able to generate profits regardless of the direction of the global economy. As a result, GlaxoSmithKline provides its investors some security.

Likewise, Johnson & Johnson holds a stable of subsidiary businesses. In fact, J&J controls more than 275 operating companies. Johnson & Johnson is organized into three main operating segments, medical devices and diagnostics, pharmaceutical, and consumer health care products. Each is highly profitable, and impressive in size.

Its medical devices and diagnostics segment lets the company capitalize on the favorable economics of an aging population. This segment is growing quickly. With $27.4 billion in revenue last year, J&J's medical devices and diagnostics segment is the largest medical technology business in the world.

The consumer segment contains several world-class brands that will be found in nearly every household. These include Band-Aids, Neutrogena, and Tylenol. Not surprisingly, J&J's consumer segment is massive, it is the world's sixth largest consumer health care business. And, thanks to the stability of consumer health care products, this segment reduces volatility in the company's earnings.

Why Pfizer is a riskier bet
Pfizer has taken a number of strategic initiatives in recent years to streamline its business. These may very well pay off, assuming Pfizer will execute on its priorities. At the same time, the fact that Pfizer's business is less integrated than its peers exposes investors to a particular set of concerns.

First and foremost is that Pfizer is now virtually a pharmaceutical pure play after spinning off its animal health care business earlier this year. Pfizer does have a consumer products business, but that segment contributes only about 6% to its overall revenue.

Furthermore, investors should be concerned about Pfizer's pipeline, as it is still struggling in the aftermath of Lipitor losing its patent exclusivity. Lipitor was the best-selling drug ever and provided nearly $10 billion in annual sales, as recently as 2011. To date, Lipitor has generated just $1.7 billion in sales, down by nearly half from the same period last year.

Overall, Pfizer saw sales fall 7% through the first nine months of the year. Earnings are up, but much of that has to do with lower expenses and a one-time gain related to discontinued operations. From a core business perspective, there are many lingering questions that Pfizer needs to address.

The Foolish takeaway
While GlaxoSmithKline and Johnson & Johnson may seem like lumbering giants, their diversified operations and steady consumer products businesses provide valuable stability. Pfizer may very well hit a home run (or several) with the billions it's spending to try to replace lost Lipitor sales, but that is far from a guarantee. As a result, you may want to assume a defensive position heading into 2014, and give GlaxoSmithKline and Johnson & Johnson a closer look among large-cap health care stocks.