A Roth is way better than a traditional IRA when you have large returns. For a traditional IRA, you still have to pay full income tax on the entire amount of your withdrawals including your original investment, whereas a Roth is completely tax free.
pez and my fellow pharmacists please listen to me because the above statement is factually inaccurate and you could compromise your lifetime returns if you acted on this with the wrong assumptions.
What the above statement misses is: 1) the returns you could get on the deferred taxes; 2) efficient tax strategies on investments (capital gains, step up in basis); and 3) potentially lower tax bracket when you retire. Let's go through a hypothetical:
You are in the 25% tax bracket and are eligible for a full tax deferral from a Traditional IRA. You can decide to put $6,000 in either a Roth or Traditional and if you do a Traditional you will invest the tax deferral of $1,500 in a taxable account. And let's say your only investment strategy is buy and hold SPY the S&P 500 ETF and let's assume the annual return is 10% in capital appreciation and 1.5% in dividends.
In 20 years, both the Traditional and Roth IRA have the same value = $6,000 * (100% + 10% + 1.5%)^10 years = $52,924. The taxable account would have to pay 25% taxes on the 1.5% of dividends so after 10 years the value grows from $1,500 to $12,369.
First off, notice the buy and hold strategy is very tax efficient. The $1,500 would have grown to $13,231 if you didn't pay any taxes so not much of a loss over 20 years.
Now let's assume you retire at the end of the 20 years and have to start taking RMDs from the Traditional IRA and your tax bracket is now 15%. For simplicity's sake let's just assume you can take it all out and pay 15% on it. That nets you $44,985. And now you selloff your taxable account for a long term capital gains tax of 15% and that nets you $10,513. Together that is $55,498 which is about 5% more than the Roth IRA.
You want even more tax efficiency? Then never selloff the taxable account and hold until you die for step up in basis 0% taxes. That yields about 8% more than a Roth IRA. And you could juice your taxable account returns by using margin. And so many more ways to play this out. And if affordability is a problem then, for example, if you were tight on cash, $6,000 in a Traditional should beat $4,500 in a Roth.
Don't get me wrong, a Roth IRA is great but if you can get a tax deferral with a Traditional IRA the answer just isn't so cut and dry.
P.S. And sometimes lowering your AGI with a Traditional IRA leads to other benefits you might otherwise miss out on, i.e. lower your student loan payment.