So this is the challenge: you can only invest in one share. You have to choose one company to buy into above all others, that you will hold until your retirement. Which is it to be?

Well, in an effort to answer this question, let’s think about what sort of company we’re looking for.

Firstly, I think I would pick a blue chip. Large businesses tend to be more stable. Small caps may grow faster, but they are unpredictable, and if I am investing for the long term I would want a company that keeps producing, rather one that could just be a flash in the pan that’s here today and gone tomorrow.

Earnings is a key criterion

Another key factor for me is earnings. I would choose a business that is consistently profitable. I would tend to avoid companies that are not currently making money but which promise to be profitable at some time in the future. I want to see real proof that this company makes money, and will continue to do so for years to come. After all, the share price is determined not by revenues, nor by number of employees, but by the amount of earnings the company makes.

Then another crucial criterion is to see the big picture. We need to look beyond the day to day movements of stock prices. What are the key cycles that are affecting this share? What trends can we take advantage of? One of the biggest trends that I think investors should buy into is the growth of emerging markets such as China, India and Vietnam. As these markets grow, a rapidly expanding global middle class will be eager to snap up consumer goods. Businesses that cater for this market are likely to do very well.

Cater for the world’s growing middle classes

In contrast, there are other sectors that are under immense pressure, such as UK supermarkets, and the retail banks. And the oil, gas and mining sector is also one to avoid, as a cyclical bear market is something I would never bet against.

So, we are narrowing it down. BP and Shell are out. So are Tesco and Sainsbury. As are UK banks like Barclays.

But what about the consumer goods firms? Well, there are the stalwarts Unilever (LSE: ULVR) and Reckitt Benckiser. Both have been growing their earnings and share price steadily over the past decade. Both are making large and rising profits. And both are big, stable firms that are likely to still be going decades into the future.

If I had to choose between them, I think I would plump for Unilever. Why? Because it has, in my view, the better brands with the greater global reach. And it is expanding rapidly in emerging markets, whereas Reckitt has much more to do in these fast-growing regions. A 2016 P/E ratio of 21.58, with a dividend yield of 3.19%, may seem fully priced, but this is one to tuck away in your portfolio, ready for your retirement.

And here are more shares to invest in for your retirement....

If you are looking for great companies to buy into as you plan for your retirement, our experts at the Fool have picked 5 excellent prospects that could make all the difference to your retirement portfolio. Unilever might just be one of them.

They are strong, stable businesses that take advantage of key trends and are likely to provide a major boost to your portfolio, in this year and beyond.

Just click on this link to read "The Fool's five shares to retire on", and it will be dispatched to you instantly, free and without obligation.

Prabhat Sakya has no position in any shares mentioned. The Motley Fool UK owns shares of and has recommended Unilever. The Motley Fool UK has recommended Barclays, BP, Reckitt Benckiser, and Royal Dutch Shell B. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.