Generally speaking, the order in which you should contribute to retirement accounts is as follows:
- 401K up to the amount required to get the full employer match
- IRA (or Roth IRA) up to the yearly maximum (currently $5,500)
- 401K up to the yearly maximum (currently $18,000)
Since you don't get a company match, eliminate step #1.
This ordering assumes that the investment choices in an IRA will be better than those in the 401K (because for the IRA you can pick a low-cost provider, like Vanguard, whereas for the 401K you're stuck with whatever your employer chooses). If that's not the case -- for example, if your IRA would only allow you to invest in
VTSMX (0.17% expense ratio) or
VTSAX (0.05% expense ratio), but your 401K allows you to invest in
VITSX (0.04% expense ratio) and doesn't have any other fees, then maxing the 401K should be done before starting to invest in the IRA.
As for Roth vs. traditional, that's a separate issue only tangentially related to the question of IRA vs. 401K. The only situation when it matters is if you determine a Roth is better for your tax situation
and you would otherwise be inclined to invest in the 401K (e.g. because it has lower expenses, as in the example above) first
and your employer does not offer a Roth 401K. In that case, the tax advantages of the Roth might outweigh the slightly lower expense ratios. However, such a situation is highly improbable. In particular, it is
never worth foregoing a company match on a traditional 401K just to get a Roth IRA instead (because the match is free money, so your marginal tax rate would have to be
so high that the tax savings would exceed the match -- which never happens).