There are benefits to both the pre-tax retirement accounts (401k, Simple, SEP, 403b, etc.) and the post-tax (Roth IRA). The nice thing about the Roth is that if your income tax rate is pretty low now, then it's a great time to get the money taxed and never taxed again. If you plan on being rich and taking out at least $100k in income in your retirement years, then it'll get taxed at whatever the capital gains tax rate is at that time. That is another good reason why you should max out your Roth IRA now if you are a young person. No one knows what the social security and federal tax rates will do in the future, but my guess is that it will go up over the next 30-40 years. They can't touch your Roth IRA money with taxes (well, I guess Congress can try, but voters aren't going to let that happen). That is security I think.
As for the pre-tax accounts, you MAY end up with a lower tax bracket in the future and you may be able to take it out at a cheaper rate.
BUT.... you should really be maxing out savings on both your pre-tax and Roth IRA at the same time. That amount is around $17.5k - $21k or so per year per person, depending on what type of accounts you or your company has and how much money you make. And if you aren't making or saving at least that much, I wouldn't worry so much about figuring out which account maxes out your returns, but how to make more money or save more money first.