The truth is that where you open an IRA matters more than you might think. From commissions to fees, and even investment choices, the differences between brokers can be numerous. But instead of focusing on every single difference, investors should compare brokers on the big items. Here's how two popular brokers, Merrill Edge and Interactive Brokers, stand on criteria that really matter to the long-term IRA investor.

Commission prices

One of the biggest differences between these two brokers is how they calculate commissions. Merrill Edge uses a flat-rate commission schedule, whereas Interactive Brokers' commissions vary by order size.

Brokerage

Stocks and ETFs

Stock Options

Mutual Funds

Merrill Edge

$6.95 per trade

$6.95 + $0.75 per contract

$19.95 per purchase

Interactive Brokers

$0.005 per share ($1.00 minimum)

$0.25 to $0.70 per contract ($1.00 minimum)

$14.95 per purchase

Data source: company websites.

Both brokers have ways for their clients to save on trading costs. Interactive Brokers' variable commission schedule promises even lower commissions, particularly for higher volume traders. Merrill Edge customers can get up to 30 commission-free trades by maintaining a minimum balance in their accounts.

Beyond these money-saving options, savvy investors should see if they qualify for some special offers, which include free trades and cash bonuses worth thousands of dollars.

Mutual fund selection and commission-free choices

You'll find that both brokers offer thousands of mutual funds, many of which can be purchased without paying a transaction fee to your broker.

Brokerage

Total Mutual Funds

No-Load, No-Transaction-Fee Funds (NTF)

Commission-Free ETFs

Merrill Edge

More than 7,600

More than 2,300

Not available

Interactive Brokers

More than 8,200

More than 2,900

41 (Global X, Cambria, and O'Shares)

Data source: company websites and representatives.

Over time, fee-free fund choices can save you a fortune, as investors who make routine contributions would be able to avoid transaction fees of $14.95 or $19.95 on each investment. 

Minimum deposit requirement for IRAs

One very big difference between brokers is how much you have to deposit to get started. Merrill Edge doesn't have a minimum deposit requirement, so you can open an IRA for as little as $1 if you wanted to. Interactive Brokers requires that investors deposit at least $5,000 to open a new IRA account. 

A jar full of coins and currency.

Some brokers require larger initial deposits than others for IRA accounts. Image source: Getty Images.

International stocks and ADRs

If you like to invest in individual stocks around the world, where you open an account may be critical to your trading strategy. The differences between international investing options are as follows.

Type of Investment

Merrill Edge

Interactive Brokers

American depositary receipts (ADRs)

Yes

Yes

Stocks traded on international stock markets

No

Yes (More than 100 markets)

Mutual funds and ETFs of foreign stocks

Yes

Yes

Data source: company websites and representatives.

Like most brokers, Merrill Edge only offers foreign investments in the form of mutual funds, ETFs, and ADRs on U.S. exchanges. Interactive Brokers opens up more than 100 markets for electronic trading, as it can route your trades to markets thousands of miles away.

Keep in mind that only a few online brokers currently offer trading on international exchanges, so international investors have fewer choices in brokers than those who only invest domestically.

Mobile app reviews

Apps for mobile phones and tablets allow you to check your balance and make trades on the go. Here's how each brokers' users and customers rated their mobile trading apps, as of Jan. 31, 2017.

Brokerage

Apple App Store

Google Play

Merrill Edge

2.0 stars

4.0 stars

Interactive Brokers

2.5 stars

4.0 stars

Data source: relevant app stores

IRA fees: Maintenance and inactivity fees

Fees that may go unnoticed on large accounts can add up quickly on smaller account sizes. Keep on the lookout for two fees: maintenance fees (for simply having an account) and inactivity fees (for trading too infrequently).

Interactive Brokers customers should be aware of its inactivity fee, which is assessed when an account generates less than $10 in commissions in any given month. The fee is added to commissions during the month so that the total equals $10. Thus, if you spent only $4 on commissions, a $6 fee would be added on top.

This inactivity fee can be avoided if you maintain a balance of at least $100,000. Merrill Edge does not have recurring maintenance fees or inactivity charges for any accounts, including Roth or Traditional IRAs.

Where to open an IRA: Interactive Brokers or Merrill Edge?

The truth is that both brokers have a lot to offer, with features that fit different types of investors. For example, high-activity traders will enjoy Interactive Brokers' low commission prices, whereas infrequent traders may prefer avoid a broker with inactivity fees. Merrill Edge's no minimum deposit requirement fits investors who are just getting started, and its generally higher commissions may be offset by the fact it doesn't require a certain level of activity.

Ultimately, it's really all about how each broker fits your specific needs. To be clear, The Motley Fool does not endorse any particular brokerage, but we can help you find one that is a good fit for you. Visit Fool.com's IRA Center to compare several brokers all on one page and see if you qualify for any special offers for opening a new account.

Jordan Wathen owns shares of Interactive Brokers. The Motley Fool recommends Interactive Brokers. The Motley Fool has a disclosure policy.