Without knowing more about your overall financial situation (e.g. age, time horizon, goals, etc.) it is impossible to say for sure.
However, if you are going to be in a lower tax bracket in retirement than you are now, it would generally be beneficial to go with the pre-tax contributions to a 401k. If you are going to be in a higher tax bracket in retirement than you are now, it woud generally be beneficial to go with the after-tax contributions to the Roth IRA. If you are going to be in the same tax bracket in retirement as you are now, it does not matter which you use.
I will posit a fourth option - if you do not know what your tax bracket will be in retirement, then it may make sense to utilize both pre-tax and after-tax options.
So, if you are a ways off from retirement (say 15-20+ years), we just don't know what tax rates will be that far out. There is a lot that can change in the tax code between now and then. So, it could make sense to utilize both pre-tax and after-tax. That will provide you flexibility in retirement as well as provide tax diversification in retirement. Additionally, if you are young, the Roth can be especially beneficial because it has even longer to grow tax-free.
In other words, I bet it would make sense to utilize both the 401k and the Roth IRA. In what amounts out of the $1,000, I cannot say (other than to note that if you are younger than 50, the max you can contribute to the Roth IRA in 2015 is $5,500 and it is $6,500 if you are 50 or older) without knowing more about the overall situation.
But, it may be worthwhile to max out your Roth and put the rest into the 401k.
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