Interactive Brokers wins once again for its huge investment selection, highly rated advanced trading platforms, impressive mobile apps and low margin rates.

Fidelity is a long-standing winner in this category. It brings rock-bottom fees, a high interest rate (and automatic sweep) on uninvested cash, a large selection of no-transaction-fee mutual funds, extensive investor education and more than 200 physical branches.

Schwab offers a wide range of IRAs, including traditional, Roth, inherited, custodial, SIMPLE and SEP IRAs. It is one of the few brokers that offers Roth inherited and Roth custodial IRAs. Schwab also offers tons of tools for retirement investors, including calculators, educational content and a self-guided digital financial plan.

Schwab's robo-advisor offers a large variety IRA options beyond traditional and Roth IRAs, including rollovers, inherited SEP and SIMPLE IRAs. The advisor also charges no management fee and offers a full suite of retirement tools, as well as a complimentary self-guided financial plan.

Fidelity Go wins this category thanks to its use of no-expense-ratio index funds, free management on balances below $25,000 and no additional account fees.

It's hard to match Wealthfront here, which is why it’s a repeat winner. The robo-advisor offers ETFs from 12 asset classes, customization options, an automated bond portfolio, cryptocurrency trusts and a socially responsible portfolio. Clients can also trade individual stocks, ETFs or REITs.

Fidelity wins again for its all-star lineup of trading tools, research providers and low fees, all offered in a highly rated mobile app that impressed our testers.