By now you've either stopped reading or are wondering what that reason is, so:
Roth retirement plans have a 25% larger effective contribution limit.
Traditional retirement plans allow you to catch up on that 25% later tax-free, possibly all at once.
If you're contributing enough money that you're bumping up against the $15,500 limit, use a Roth.
If you're not and there is *any* chance you might ever come into a windfall (like an inheritance) that you'd like to be able to invest in a tax-advantaged way, use a traditional IRA (or 401k).
When that windfall comes (or perhaps in the following tax year, if it's a taxable windfall), convert the traditional retirement plan to a Roth. The conversion is a prepayment of all the taxes that will ever be due on that money -- but it has the effect of making all the income on the retirement money tax-free going forward, so it's a great investment. And the tax payment doesn't have to come from the IRA; it can come from the windfall.