If your tax bracket remains the same then the value of an invested dollar (adjusted for your taxes) in either a Roth or a traditional IRA is the same (between when you invest it and when you take it out). Note that in a ROTH the taxes are paid up front when you earn the money. In a traditional IRA the taxes are paid when you take the money out.
So for example if you are in a 25% tax bracket and put in $1000 into a traditional IRA, you could deduct that $1000 off your taxes and only have a real cost of $750. Well lets say you leave it in for a couple of decades and that $1000 (pre-tax) money has grown ten times to $10k. You take the money out and pay taxes and keep $7500 (after tax money). Now lets suppose that you had funded that Roth IRA with the equivalent cost to you of $750. That money then grows ten times to $7500 and you then take it out and have $7500 to spend. Can you see from this example how the traditional and Roth IRA give you the same returns considering the tax-adjusted doallrs that are put in and that are subsequently taken out. It is only when tax rates change that one or the other makes a difference.
One advantage of a ROTH is that since you are putting in after-tax money that vehicle allows you to put in more (after tax money) than the tax-discounted traditional IRA. (ie. $5000 in a traditiona IRA needs to be discounted by your tax bracket to maybe $3750). The ROTH IRA lets you put in the full $5000.
All things being equal, many people move into lower tax brackets after retirement. That may not always be the case for people that continue to work and save or for people that or that strike it big (inheritance, lottery, super big investment returns).
If you believe that you will be in a lower tax bracket when you pull the money out of the IRA then a traditional IRA is the way to go. If your bracket will be higher then a ROTH is the way to go. As posted above future tax brackets are unknown so you have to estimate (guess) what they will be.
There are also some trust issues in that you are trusting the government to keep the rules the same for decades to come. You can game the system now under the current rules. However if the rules change then who knows
There are also some differences between the two plans in terms of someone inheriting them. Also some differences in required distributions when you hit your 70's.
here is one (of many) available articles that discuss the choices.
http://www.investopedia.com/articles/retirement/03/012203.asp?viewall=1