It's been a while since I did primary research on the topic; I decided on a Roth for my personal circumstances and dumped most of the other knowledge afterward, so I'll be deferring to references: here are a couple articles about the topic of choosing between them, one which links to a calculator.

You measure tax efficiency by what percentage of the money you get to keep after it's been taxed in the context of your other income and investments. Putting tax-inefficient funds in tax-efficient formats like an IRA lets you keep a (hopefully much) larger percentage.

And I don't see how it's off topic in an Open Thread.