There are plenty of stocks to buy from, but these 10 stocks are in the best form.

The 10 biggest companies in the S&P 500 index are collectively worth $4.36 trillion. The entire S&P 500 recently topped $20 trillion in value for the first time.

So the top 10 companies, a mere 2% of the 500 stocks in the index, make up almost 25% of the S&P 500's total market value. That is incredible.

The rise in popularity of index ETFs that track the S&P 500 is one of the reasons why these 10 stocks are so widely held.

But the massive importance of the biggest 10 companies is also a reflection of how many investors like to follow the old motto of former Fidelity markets guru Peter Lynch: Buy what you know.

Brand name tech companies dominate the market these days. Apple is the most valuable company. It's now worth more than $700 billion.

Google owner Alphabet, Microsoft, Amazon and Facebook are the second, third, fifth and sixth most valuable stocks.

These five companies are ones that most people interact with constantly in their daily lives on their smartphones.

The only non-tech in the top six is run by a well-known Luddite of sorts - Warren Buffett's Berkshire Hathaway is fourth. But even Buffett realizes that tech is an area you can't avoid. Apple is now one of Berkshire's top holdings.

The remaining stocks in the top 10 aren't tech giants, but they are all leaders in their respective industries and are companies that are not too hard for average investors to understand. Cable and entertainment giant Comcast is seventh. Exxon Mobil, JPMorgan Chase and Johnson & Johnson round out the top 10.

But what will happen if any of these 10 mega stocks suffered a massive drop because of poor earnings, accounting problems or management scandals? Surely, they could risk bringing down the entire market because of their popularity.

So, investors will hope these 10 companies are here and will not create any big crisis in the future.