Now that 2013 is in full swing, it's a great time to reassess your portfolio to ensure it isn't missing a key growth component for the year ahead. This time also provides an excellent opportunity to clean up that watchlist of yours. The best planning always starts with research. Even with its $700-plus price tag, Google (GOOGL -1.62%) deserves your attention in 2013. That's because Google tends to dominate wherever it competes, a quality that isn't likely to change in 2013. Without further ado, here are the four best reasons why you should buy Google in 2013.

1. Search leader. Google commands a relatively stable 66.7% market share of search in the U.S., and between 80% and 90% of worldwide share, depending on whom you ask. This dominance helped drive 19% year-over-year revenue growth in advertising last quarter. Search queries expected to grow as more emerging market Internet users begin to reap the benefits of the Internet. In other words, Google is in great position to benefit from this continued megatrend in the making.

2. Effective business model. According to WordStream, Google's advertising effectiveness is three times the industry average, due to its ability to better determine intent. When you search with Google, it can derive some insight of your intent. Should it be commerce related, it's basically a slam-dunk opportunity for the King of Search to serve ads worth clicking. The one caveat: the increased use of mobile search on smartphones has put pressure on its cost-per-click by 8% after adjusting for currencies. The good news is that aggregate paid clicks are on the rise, up 33% from the previous year. As Google better adapts to this mobile opportunity, combined with more Internet users coming online, this decline in cost per click should be relatively short lived.

3. Mobile OS domination. Android OS commanded 75% of worldwide smartphone shipments in Q3 of last year, per IDC estimates. According to analytic firm Distimo, Google Play's daily revenues are now growing more than two times faster than Apple's iOS. At this rate, it's just a matter of time before its $3.5 million daily revenue surpasses Apple's $15 million daily rate. Google is in a position to drive increased mindshare among emerging-market users, which may lead to expanded business opportunities as these economies continue to prosper.

4. One word: YouTube. In the U.S. alone, this beast of a platform served 13.2 billion videos to 153 million users for the month of December. No other platform compares to YouTube in terms of size and engagement. The average user streamed videos on Google-branded properties for over 388 minutes. Even if you combined the other top 10 sites, it doesn't match this level of engagement.

According to eMarketer, online video will prove so disruptive that TV advertisers will have no choice but to embrace it. It expects U.S. online video ad spending to grow by 41% this year to $4.14 billion, representing only 6.2% of total TV ad spending. By 2016, eMarketer expects online ad spending to reach $8.04 billion, making up 11% of total TV spending. In other words, the more Internet streaming proliferates, the greater chances YouTube will reap some of those benefits.

Buy with patience
Google currently has over $45 billion in cash on its balance sheet, giving it the necessary resources to deliver big returns for investors. Shares are currently trading at 23 times trailing earnings, and analysts expect Google to grow its earnings an average of 13.4% for each of the next five years. On a historical basis, Google has grown its earnings by an average of 24.5% for the past five years. These ratios indicate that shares are fairly valued relative to its earnings history, but are overvalued on a forward-looking basis. I tend to favor history over assumptions, as history gives you the facts.

In the case of Google, its fundamentals reach far beyond financial ratios. The company's strategic positioning is what sets it apart from its peers. It's operating in extremely high-growth sectors of the global economy and commands dominating positions. If these bets pay off, Google shareholders should be handsomely rewarded in the long run.