I would also recommend Betterment.
However, I would qualify that by saying that it's very difficult to rank robo-advisers (or more specifically, tech-enabled actively-managed, investment funds that charge a management fee) at this point in the game on the measure of the quality of financial returns - simply because these apps have not been on the market long enough to generate sufficient long-term return data required to evaluate their effectiveness at generating long-term capital gains (their intended value proposition).
That said, the functionality, user experience & design of Betterment is pretty stellar. Here's why:
• The Onboarding Questionaire - this helps Betterment tailor your experience & suggested strategies to match best practices for someone in your financial situation & with your financial goals.
• AutoDeposits - the ability to set up recurring transfers from your bank account into your Betterment accounts makes saving automatic & simple, and less subject to one's ability to remember to deposit into his/her savings or to irrationality that may steer one off his/her original savings plan.
• Separate fund buckets - the ability to allocate your investments between a Retirement account (for retirement of course), a Safety Net (in the event you are laid off, or otherwise need some financial backup for a rainy day), Roth IRA, and Traditional IRA, allows one to set multiple investment strategies to match the purposes of the different sub-accounts (eg. heavier allocation into Stocks for the Retirement account for a young user vs. a heavier allocation into Bonds for the Safety Net account, or for users who are closer to retirement and desire security over larger upside.
• Portfolio Allocation - the ability to change the relative % of your portfolio that goes into Stocks (generally riskier) vs. Bonds (general considered safer) allows one to invest according to one's own risk preference & goals for each of the sub-accounts .
• Tax optimization guidance - I believe Betterment works hard to make sure your investments are done in a way that keeps taxes on your gains at a minimum
For these reasons, I've been giving Betterment a try since about August 2015 (I think I'm up 7.7% since that time, time-weighted, which I can't complain about.
It really depends what you are looking for in a robo-adviser. There is no "silver bullet" robo-adviser that I'm aware of that is going to satisfy all your personal financial needs (managed fund investing, individual stock investing, passive index fund investing, portfolio assessment & allocation, and budgeting, etc.)
But Betterment seems pretty effective so far at helping users save for retirement & rainy days in a way that matches their stage in life and risk appetite.