In addition to the excellent answers provided by the other advisors here, I'd like to elaborate a little bit on the point regarding early withdrawals, as well as a quick point regarding estate taxation.
Direct contributions to a Roth IRA may be withdrawn without tax or penalty at any time. No such provision exists for traditional IRAs.
Distributions from a Roth IRA may be "qualified" or "non-qualified" (mainly related to whether you are over or under 59.5 when you take the distribution, but there are other qualifying circumstances as well). Non-qualified distributions may or may not be taxed or penalized, depending on the source of the distribution.
Regardless of the order in which money is added to the Roth IRA, the IRS uses "ordering rules" to apply to the distributions, and they come out in the following order: 1. all regular participant contributions; 2. taxable conversions/rollovers; 3. non-taxable conversions/rollovers; 4. earnings on any of the previous contributions.
To the extent that a non-qualified distribution is just the return of regular participant contributions, the distribution is nether taxed nor penalized.
Additionally, taxable conversions/rollovers, since taxes are paid at the time of conversion/rollover, do not get taxed, and if it's been 5 years or more since the conversion/rollover, there's no penalty, either.
The upshot of all this is that if you are able to make direct participant contributions to a Roth IRA, there's no downside - you can always get that money back out without taxes or penalties.
As far as estate taxation, while this is a lot less of a concern now with the very much higher estate tax exemption (over $5 million per person), if there is any expectation of the estate being taxed, it's much better to have Roth assets rather than traditional IRA assets inasmuch as the estate tax applies to the account value without regard to the fact that the money is pre-tax or after-tax (traditional vs. Roth). Which means that if you have $1000 in a traditional IRA and you face estate taxes, you owe estate taxes on that full $1000 -- even though after the death in question, you'll pull that $1000 out and pay incomes taxes *again* on it. In other words, if your heir's marginal tax rate is, say, 30%, then you'll be paying estate taxes on the $300 which is the part which will be going to pay income taxes. Taxes on taxes. If the owner had $700 in a Roth IRA rather than the $1000 in a traditional IRA (assuming same marginal tax bracket), then only $700 would be subject to estate taxes - no estate taxes apply to the part which was already spent paying income taxes.
Again, the estate tax issue is not going to affect nearly as many people now as it would have had they not come to terms making the higher exemptions permanent, but it is something which was a big issue a few years ago, and which high-net-worth folks should remain aware of. It makes it worthwhile for high net worth folks to consider Roth conversions and paying taxes now, even at higher marginal rates than their heirs may eventually face.