After narrowing the field, it's time for the first buy for our Rising Stars "multivitamin" portfolio. If you can pretend for a moment you didn't read the headline, I'll masterfully build the suspense for you. For background on exactly what type of company we're seeking for the first buy, it might help to read last week's article.

Beyond the numbers
When last we talked, Microsoft (Nasdaq: MSFT) easily had the best numbers of the bunch. Not only did it have the best margins and returns on investment, it also carried the best valuation. But now it's time to open the hood and look at the nuts and bolts of our candidates' business models and competitive positions.

Actually, we can be fairly confident in the soundness of any of these business models. Like the final contestants of a beauty pageant, our screening process ensured we were only left with the most talented companies (OK, bad example). Microsoft, Coca-Cola (NYSE: KO), PepsiCo, Procter & Gamble (NYSE: PG), McDonald's (NYSE: MCD), Abbott Labs (NYSE: ABT), and 3M (NYSE: MMM) are all rock-solid financially and have a strong history of earnings and dividend growth. All have very attractive -- if not outstanding -- net and free cash flow margins. And they've all been around a long time -- four of them were founded in the 1800s!

One other major consideration: It's easy to understand all of these businesses. There are no financial firms here with arcane inner workings where even the CEOs aren't quite sure what they have. We can conclude our candidates are all well-managed and have no major flaws in how they run their businesses.

Of moats and men
Competitive positions can change over time, however, which brings us to my biggest concern with Microsoft. Its moat is under assault from all directions from the sharpest of competitors. From Google in search and productivity apps to Apple in computers, OS software, and mobile, there is no relief. This is the main reason the stock is priced so low -- Mr. Market is telling us it's not quite sure what's going to happen over the next three to five years, much less the next three to five decades.

I like Microsoft. Heck, I own shares of Microsoft and think many of these concerns are overblown. I struggled with this buy decision for days. However, my goal for this first purchase is to deliver a corporate El Dorado that has a good shot of anchoring our port for years to come. In his exhaustive research of these top-performing companies, Jeremy Siegel says "investors should be willing to pay 20 to 30 time earnings" for such El Dorados. Also, no tech firm made his list. And so Microsoft, while I think it shows good short-term potential, carries too much risk for our purposes and isn't yet at that "set and forget" level. This portfolio will be buying all kinds of stocks in the weeks to come, and Mr. Softy may well fit into another mold -- but today we're passing.

It's the real thing
Using the criteria I've set forth, I think the most attractive buy right now is Coca-Cola. Not only does it carry every single corporate El Dorado characteristic, it already is one -- and was the sixth-best performing S&P 500 firm in Siegel's 1957 to 2003 study period.

This sweet business of selling flavored sugar water at high margins ... well, it's a sustainably great business model. People everywhere love Coke, and it's one of the top brands in the world. It's the kind of brand that builds the moat that keeps thirsty consumers coming back time and again, paying a premium to have a Coke and a smile.

Besides Coke products, the company also has such famous brands as Fanta, Sprite, Fresca, Powerade, Minute Maid, and Dasani. The business consists mostly of selling concentrates and syrups to independent bottlers (including Coca-Cola Enterprises (NYSE: CCE), which is nearly 50% owned by Coca-Cola), which then produce the finished beverages, package them up, and sell them to distributors. Nearly three-quarters of Coca-Cola's revenue comes from overseas.

One of the company's self-identified core capabilities is consumer marketing, "designed to enhance consumer awareness of and increase consumer preference for our brands." Advertising expenses came to about $2.8 billion in 2009, but that's money well spent. The strong brand that this marketing has carefully crafted over the decades raked in more than $7 billion in free cash flow in the past 12 months alone. That cash flow is powering a dividend that has increased an incredible 48 years in a row.

Let's drink
I'm happy to make Coca-Cola the first purchase in the multivitamin portfolio. With $17,000 to invest over the first year, I'm initially setting $1,000 as a "full position." To start, then, I'm buying a half position -- or $500 worth. I think a half position is never a bad idea, especially for beginning or intermediate investors. Buying just half allows you to watch the company and learn, and then to allocate more to the position when conditions warrant. My buy order goes in tomorrow with -- and this is very important -- instructions to reinvest all dividends.

Remember, you can get more details on the portfolio and contribute your opinion by visiting our discussion board. See you there!

Fool analyst Rex Moore is now available in living color. He owns shares of Microsoft and Procter & Gamble. Google, Coca-Cola, 3M, and Microsoft are Motley Fool Inside Value picks. Google is a Motley Fool Rule Breakers selection. Apple is a Motley Fool Stock Advisor recommendation. Coca-Cola, PepsiCo, and Procter & Gamble are Motley Fool Income Investor selections. The Fool owns shares of and has written covered calls on Procter & Gamble. Motley Fool Options has recommended a diagonal call position on Microsoft. Motley Fool Options has recommended a diagonal call position on PepsiCo. The Fool owns shares of Apple, Coca-Cola, Google, and Microsoft. 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.