The robo-advisor sits in the middle of a three-way choice, and the middle is not automatically the right place to be.
DIY is the cheap end. A three-fund portfolio of broad index funds costs roughly 0.00% to 0.04% a year in fund fees at any major brokerage, with no advisory fee, and modern platforms automate the recurring purchase. What DIY does not automate is rebalancing, tax-loss harvesting or the moment of panic in a drawdown; those stay your job. If the head-to-head between the two big independents is your actual question, our Betterment vs Wealthfront guide prices that matchup in detail, including Betterment's $5 monthly fee below $24,000, and the same guide shows what the DIY alternative costs.
A traditional human adviser is the expensive end, commonly around 1% of assets a year for ongoing management, or flat project fees for advice-only planners. Against a robo at 0.25%, the human costs four times more for portfolio management that is often functionally similar. What a good human adviser adds is not portfolio construction but everything around it: tax sequencing, estate questions, insurance gaps, and talking you out of expensive decisions. People with complicated finances can get their fee's worth; people with a salary and an index fund usually cannot.
Whichever layer you pick, the account wrapper decision comes first, because tax treatment beats fee treatment: a robo running a taxable account for someone with unused IRA space is optimising the wrong variable. Our best Roth IRA accounts comparison covers the wrapper, and every robo on this page will run inside an IRA as happily as a taxable account - noting that tax-loss harvesting, the most-marketed robo feature, does nothing inside an IRA because there are no taxable gains to offset.