I put a small IRA in the Schwab robo-advisor as an experiment. For the most part, "robo-advising" is simply a fancy way of having an account that automatically rebalances in some formulatic way.
Schwab has you set a risk tolerance that you can adjust up or down based on preference.
What do you think of the service so far?
No complaints. My money has been there since June 2015. There's been times where it outperformed the market and times when it underperformed the market, which will be true of any portfolio that is different than "the market". Having a background in finance, I can say the approach to portfolio building from any of these services is fundamentally sound. The only reason I went with Schwab over the others is because I already had an account there. I don't think I'll move other accounts there just because my personal preference to be personally involved in investing.
While there are plenty of internet warriors that will tell you Wealthfront/Betterment/Schwab is best and all the others are the devil, the practical differences are so minor as to be immaterial. Some will outperform others, but only time will tell which ones. Be aware that Betterment has better marketing than the rest. I strongly suspect Betterment pays much higher commission rates to bloggers than Wealthfront. This isn't to say the product is better or worse. Just realize the blog recommendations are likely biased.
I strongly recommend any of these product (whichever suits your personal preference) if you're the type of person who wants to be hands-off in your investments.
Personal Capital does have a different approach than the others. Putting on my finance theory hat, Personal Capital has built an optimal individualized index fund. It's pretty cool. The only problem is that their service is the most expensive. And while it's theoretically superior, the price point is a pretty serious drawback.