Telecoms are the bread and butter of solid retirement portfolios. Because the capital requirements to building out nationwide networks are so onerous -- and the service these companies provide so necessary -- they make for protected money-printing machines once established.

That means outsized dividends. The two communications companies we're focused on today, Verizon (NYSE: VZ) and CenturyLink (NYSE: CTL), have such payouts -- yielding 4.7% and 14.7%, respectively. For investors, it might seem like money actually is growing on trees.

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But which of these two is the better buy today? That's impossible to say with 100% certainty. But by comparing them on a series of three key aspects of their stocks, we can get a better idea of what we're getting when we buy shares. Here's how they stack up.

Sustainable competitive advantages

If you're a long-term, buy-to-hold investor -- and that's what we think you should be here at the Motley Fool -- there's nothing more important to investigate than the sustainable competitive advantages -- otherwise known as "moats." In the most basic sense, a moat is what keeps customers coming back to you year after year while holding the competition at bay for decades.

One key moat all telecoms benefit from is very high barriers to entry. Because of the costs associated with setting up a telecom company -- laying down the wire, building or leasing towers, etc. -- this isn't a terribly crowded field. But because both of these companies are already established, it really isn't a differentiator.

Instead, we can simply look at market share and the different approaches each company is taking toward the future.

According to Statista, Verizon is the largest wireless subscription provider in the United States, with a 35.7% share. In addition, the company is making moves to become a more robust media player. This includes the acquisitions of AOL and Yahoo!. That gives Verizon more flexibility moving forward.

CenturyLink, on the other hand, doesn't even move the needle on a nationwide scale when it comes to market share. Instead, its future is intertwined with the recently completed merger with Level3 communications. As a Tier One provider of internet services via this move, CenturyLink has become one of the largest internet providers in the country, helping it to secure a recent contract with the Commonwealth of Pennsylvania that sent shares soaring.

In the end, it's too close to call a serious winner. As wireless contracts become progressively weaker, market share matters less for Verizon. And it's simply too early to tell if the Level3 merger will produce lasting and sustainable benefits for CenturyLink shareholders.