Online discount brokers make saving for retirement easier than ever before. When you open an IRA account through a brokerage service, you will have access to thousands of investments, from stocks to funds, and everything in between.

But where you decide to open an account matters. Different brokers cater to different kinds of customers, and each has different prices and even a different assortment of available investments. Below, we'll compare two popular brokers, TradeKing and Capital One, on key features that are most important for IRAs.

Commission prices by investment

The bad news is that it costs you something to make a trade. The good news is that it costs a lot less than it used to. Commission prices are generally dropping across the industry, and many discount brokers are now priced within a few dollars of their peers. As you'll see from the table below, just $2.00 separates TradeKing and Capital One when it comes to stock and ETF trades.

Brokerage

Stocks and ETFs

Stock Options

Mutual Funds

TradeKing

$4.95 per trade

$4.95 + $0.65 per contract 

$9.95 per purchase

Capital One

$6.95 per trade

$6.95 per trade 0.75 per contract

$19.95 per purchase

Data source: Company websites.

Keep in mind that the table shows each broker's standard rates, which are frequently higher than the effective average trading price. Thanks to commission-free funds and special offers for IRAs, the true cost of the average trade can be much lower than the standard price.

Mutual funds, ETFs, and commission-free choices

Brokers often differentiate themselves in fund selection by offering more or fewer funds, some of which may be available for investors to buy without a transaction fee. TradeKing and Capital One offer thousands of mutual funds and ETFs, but you'll pay a fee to buy most of them.

Brokerage

Total Mutual Funds

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

Commission-Free ETFs

TradeKing

More than 12,100

None

None

Capital One

More than 1,100

More than 400

None

Data sources: Barron's , company websites, and representatives.

Depending on how important funds are to your portfolio, either broker may have an advantage here. Notably, Capital One has fewer mutual funds, but it does offer funds that you can buy and sell without paying a commission. That said, for any fund that isn't free, TradeKing's standard commission price of $9.99 is lower than Capital One's rate of $19.95.

Minimum deposit requirement for IRAs

Neither Capital One nor TradeKing have a minimum to open a brokerage account for your IRA. That said, it can be advantageous to get started with more than just spare change.

Some mutual funds have their own investment minimums, and you'll need to be able to afford at least one full share of a stock or ETF to make your first investment. Besides, some brokers will give you perks like commission-free trades or bonuses for depositing more than the minimum when you open an account.

Coin jar spilling outward

Image source: Getty Images.

International stocks and ADRs

If international stocks are a big part of your investment strategy, you may have to be more selective when it comes to a brokerage firm.

Neither Capital One nor TradeKing offer the ability to send trade orders to markets overseas, but both allow their clients to trade American depositary receipts (ADRs) that trade over-the-counter or on American exchanges.

In simple terms, this means that investors can usually invest in the world's largest companies through an ADR, regardless of the broker they pick. However, smaller foreign companies are less likely to have an ADR, and can only be traded by sending trades to their home market. If you'd like to trade stocks on markets around the world, you'll need a broker that offers that capability.

Mobile app reviews

You can check your account and make trades from your mobile phone or tablet from anywhere around the world. Here's how each broker's users and customers rated their mobile trading apps, as of March 8, 2017.

Brokerage

Apple App Store

Google Play

TradeKing

1.6 stars

4.1 stars

Capital One

2.5 stars

2.9 stars

Data source: Relevant app stores.

Fees on IRA accounts

Not all accounts have fees, but two types of fees are common in the industry. Maintenance fees, also called service fees, are the price you pay to have an account. Inactivity fees are charged to clients when they do not meet a brokers' minimum activity requirements.

Capital One doesn't have either kind of fee. TradeKing has an inactivity fee, but you won't be charged a fee for inactivity if you keep a balance of more than $2,500 or make at least one trade per year.

How TradeKing and Capital One compare for IRAs

Depending on how you plan to manage your account, either broker could be the better pick. TradeKing offers some of the lowest standard commissions, particularly when it comes to mutual funds, but it doesn't have any fee-free funds that many other brokerages offer. Capital One has higher standard prices for stock and ETF trades, but it offers a lower-cost Sharebuilder service and has more than 400 funds you can invest in without paying a commission.

To be clear, The Motley Fool does not endorse any particular brokerage, but we can help you find one that's 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.