In this world of ubiquitous ATMs, tap-to-pay checkout and automated bank deposits, there are still times when it's necessary to hand over, or collect, hard cash. That's why money-transfer services Western Union and MoneyGram have tens of thousands of agents in cities and towns around the world.

Money-sending services can be a lifesaver. You may feel it's unlikely you'll ever be broke and stranded in a bus station in Bengaluru, needing your spouse to send cash, but stranger things have happened – and not just when you're traveling abroad. How about when your kid, who's gone off to study at a Canadian university, needs you to send rent deposit – pronto? More routinely, money-transfer companies provide banking services like money transfers, money orders and bill payment to people who don't have bank accounts. In the United States and Canada, many customers are new immigrants who send money regularly to family members in their home countries. Outside the U.S., it's even easier to find a nearby agent for Western Union (WU) or MoneyGram (MGI) or both. Cash is still king in many countries, and in developing nations many people don't have bank accounts.

So which is better, MoneyGram or Western Union?

There is now actually a big three in the money-transfer business: Western Union, MoneyGram and Wal-Mart (WMT), with the retail giant recently big-footing into this business. (Its service is currently limited to in-store domestic transfers, while its international and online transfers are handled by MoneyGram.) (For more, see Find The Top Money Transfer Services.)

In the U.S., Western Union or MoneyGram services are available in many pharmacies and supermarkets as well as small local businesses, bus stations and check-cashing outlets. For most of these agents, handling money transfers is a side business. Wal-Mart, of course, offers its service in its stores.

One drawback to sending cash through these services is that they open or close with the shops' usual hours. You may have to cool your heels at the bus station until the next morning before your family can get you that emergency cash.

The biggest drawback of any money-transfer service is the vulnerability of its customers to fraud. A request from a stranger for payment via cash transfer is usually a fraud. Since the recipient is untraceable, it's the modern equivalent of stuffing a wad of unmarked bills into an envelope and leaving it in a public place on instructions from a stranger.

There are a few differences between the services:

Western Union is the larger of the two companies and has instant name recognition around the world, thanks to its one-time monopoly of the telegraph business. Sending telegrams was discontinued only in 2006, but by then Western Union had moved on to new ventures. It has about 400,000 locations around the world. Customers can send money by phone, through the Western Union website or in person.

Fees can be steep or cheap, depending on a long list of factors including the form of payment used, how fast the money is delivered, whether it is paid in cash or wired to a bank, where it's sent from and where it is delivered. For international transfers, the exchange rate adds another element of uncertainty to the cost.

Say you are in Philadelphia and want to get $500 delivered to someone in Mexico. If you pay cash at a Western Union agent, and the recipient picks it up in cash, it costs $28 for three-day service, and $40 for immediate delivery. The same transaction costs $5 if it is a bank-to-bank transfer, or $25 if a credit or debit card is used to pay money into a bank account. The most cost-effective way to pay is online or via the mobile app, where fees for most of the above variations are only $4 to $7. But even using the mobile app, if you're paying with a credit or debit card, and the money will be picked up in cash, the fee for that $500 transfer is a steep $45.

MoneyGram is Western Union's biggest rival, and its fees are often cheaper. It recently changed its fees to a flat rate of $11.50 for transferring $50 to $900 within the United States, and 2% for amounts over $900. But MoneyGram built its reputation on international money transfers. It has 25,000 payment locations in Africa alone.

MoneyGram's rates for international money transfers don't appear to be much simpler than Western Union's. You can transfer $500 to Mexico, even using a credit or debit card, for a $6.65 fee, but the same transaction costs $29.45 if the money is picked up in Ireland, and $23.75 if it goes to China.

Another big difference: For now, MoneyGram transactions can be initiated only in the United States and a handful of other countries, although it claims some 350,000 locations around the world for pickup.

Wal-Mart offers a lower price than its rivals in this area, but its in-store service is limited to transfers within the U.S., using cash, a debit card or a WalMart MoneyCard. (International money transfers are available in the stores and the website through MoneyGram.) Its fees are currently $4.50 for up to $50, and $9.50 for up to $900.

The many pricing variables make it impossible to state whether Western Union, MoneyGram or Wal-Mart is the best, or even cheapest, service available.

It's safe to say this: If your kid is 1,000 miles away at an American college and desperate for cash, the easiest, cheapest and fastest thing to do will usually be to drop by a Wal-Mart. But it's faster, and almost as cheap, to use MoneyGram online, since you're sending money within the U.S.

If you're sending money to someone in Beijing or Djibouti, and it's not an emergency, check the fee calculators on Western Union and MoneyGram to see which one has the better rate for where you are, where you're sending money, how much you're sending, what form of payment you're using, how you want it delivered and how fast. The fee estimators display the exchange rate used on that day, and it's best to check that, too.

But if your husband is stuck in a bus station in Bengaluru with no money, you need to use whichever of those two companies' names pops into your head first, and get the job done.

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