The general investing strategy is that you want to use tax-advantaged accounts first before anything taxable. It's to my understanding that Betterment serves as a taxable account, so I would move that out into a tax-sheltered account.
Examples:
A 401(k) allows you to decrease your taxable income by your contributions. The max is $18,000 for this year. This $ will be taxed when you take it out.
A Roth IRA lets you contribute up to $5500 per year and grows tax-free (because you are contributing to it with money that has already been taxed).
An HSA lets you contribute $3350 per year if you have a high deductible health insurance plan. This money can be invested if you wish.
My thinking is that you should contribute to one or more of these. The general totem pole is this:
-401(k)
-Roth IRA/Traditional IRA
-HSA
-Taxable
Ideally you should be doing the first three. But that would be $18,000 + $5,500 + $3350 which is a lot of income to be stashing away. It looks like your income is about $55,000 whereas your expenses are only $15,000. Seems like you'd be able to do all of these tax-advantaged accounts, which is fantastic.
Not only that, but the 401(k) and HSA contributions would be deducted from your taxes. This effectively makes your income $55,000 - $21,350 = $33,650. That puts you in a pretty low tax bracket even though you're stashing away a lot. :)
If you want to pay off loans, that's possible too. There's a way to get the right strategy for your case.
Edit: I agree with everything MDM said as well, I just went into a bit more detail.