Both employer sponsored retirement accounts and IRAs provide the option to save in either Traditional accounts or Roth accounts. The main difference between the two accounts is when income tax is collected. In a traditional account, you put pre-tax income into the account and contributions and savings grow tax-free until you withdraw them in retirement. At that point, income taxes are assessed on the total amount withdrawn.
In Roth accounts, tax is collected up front. That means that contributions made to Roth accounts are post-tax. Savings in these accounts also grow tax-free until you withdraw them in retirement. No taxes are collected on withdrawals though.
If you expect to make more in retirement than you do now, a Roth account may be a good option. For instance, if you are younger and expect to advance significantly in your career or if you are taking time off for school or travel, paying taxes in a lower tax bracket now may be more helpful than decreasing your current income, so a Roth account would be a good option. The opposite is true as well. If you plan to cut back on expenses in retirement and withdraw less than you earn now, saving in a traditional account might be more effective.