Low percentage of active duty contributors to the TSP

Throughout my military career, I have had many leaders recommend investing in the TSP.  I never wanted to because it didn't seem like the best investment option because investors will need to pay taxes on the earnings when it is withdrawn in the future.  Since October 01, 2012 the Army has had a Roth TSP in place.  To me, this seems like a much better investment option for a majority of Soldiers because contributions are already taxed at the investor's current tax rate, but will be tax free upon withdrawal in the future.  Since many Soldiers pay such a low tax rate (factoring in the already low tax rate due to income level, the earned income tax credit, any child tax credits, and any education tax credits), that this can be a virtually tax free way to invest.

Do you invest, and if so, do you use either of these options or do you use another method to invest?  I use the Roth TSP and have realized about a 6% gain since starting in Oct 12.