So Close has a point that you should probably also be asking yourself whether or not the traditional contributions will be a better choice.
For most people a traditional IRA is like the government matching 25 cents to every 75 cents you invest. The drawback is not having any basis in your stocks, so you will pay more taxes in the future than a roth. However in the meantime you have a quarter(depending on tax bracket) more principal that hopefully appreciates. The income deferral is more valuable the longer you plan to hold these accounts before withdrawing.
Traditional IRA's also will not be taxed to the extent of your deductions and exemptions, so a pure Roth portfolio is not tax efficient. Ideally you can pull enough money from your traditional accounts to offset your deductions and exemptions and the rest from your Roth allowing you to pay zero income tax.
Another thing to consider is traditional accounts can be converted to Roth accounts at a discount during recessions. For example you can take advantage of the tax deferral now and when the market takes a 40% dip during your retirement you can convert your traditional accounts to Roth and only pay income tax on your 60% reduced value. Then when the market appreciates back to normal levels you have a greater balance in your Roth and you were able to benefit from many years of income deferral from the traditional accounts. A more conservative approach, that is not based on market timing, is pulling money from the traditional accounts during "perceived" dips and from the Roth during more stable times.
As far as choosing to use a Roth Ira or a Roth 401k; I would choose the one with the lower expense ratios. Its also worth mentioning that being able to contribute up to 53k in a Roth 401k for someone who is not self employed is a relatively new concept and its based on how the IRS will treat these accounts currently. This may change in the future, because its not based on law enacted by Congress but an interpretation of a regulating body(which is easier to change). The Roth Ira has a longer history of favorable tax treatment, so there's a better chance of it lasting the test of time. This will probably not be an issue, but since the majority of the nation would not care if the government ended up taxing the perceived rich peoples 53k Roth plans when Social Security is crumbling it may be worth considering(I would still choose based on lower expense ratios, because the chances of this happening are remote).
As I build income I am planning to max-out the following accounts in the following order:
1. HSA account(adjustment to income going in with the potential to receive roth treatment if used for medical expenses. Becomes a traditional retirement account at age 65.)
2. Max out traditional 401k for my whole life(job has Vanguard with low expense ratios and some matching)
3. Traditional IRA with Vanguard until income phaseout(Since I will be maxing out 401k with traditional I will not need to worry about phaseout until I am making over 80k)
4. 401k Roth(this will come before the Roth IRA mainly because I will be using the traditional IRA and I will have a lower expense ratios than Vanguards private accounts)
5. Roth IRA(I will start making contributions to this account when I no longer or partial qualify for the traditional IRA. I will probably prioritize 401k Roth since it has lower expense ratios)
6. If you are going for early retirement you will also need money in taxable accounts, so not many people can max all these out and still achieve early retirement. Roth IRAs do allow you to pull out the principal tax free(not sure about 401k roth), so the Roth account may be more favorable for an early retiree who will need money before age 65.
I am not an expert, but this is my advice based on my current knowledge. I always welcome feedback as my retirement plan is always evolving.