First off, good job on saving so much by 25!
For the best way to allocate, that depends a lot on your risk tolerance. I've got most of my taxable funds in Vanguard's Total Stock Market Index Fund, with about 10% in their total bond market index for some diversification of asset classes. And I recently diversified again with the purchase of a rental house. So a lot depends on what you want to do, how active you want to be in managing your money, etc. I've also been following MMM in his Lending Club experiment, so that's an option if you want a higher return in exchange for more work up front and somewhat more risk.
Overall, I'd just make sure your asset allocation matches your risk tolerance and make sure you're paying the lowest fees you can on them.