If your employer doesn't offer a 401(k) plan, a Roth IRA is an excellent alternative. You may consider a Roth IRA even if your employer offers a 401(k) because of the minimal fees and greater investment and withdrawal flexibility.
Importantly, you don't have to choose between the two. You can contribute to both a 401(k) and a Roth IRA. Even if the fees on your 401(k) are high, it's worth contributing at least enough to get the full employer match, which will more than offset the additional costs of a 401(k).
Contributing to both will also diversify the tax treatment of your withdrawals in retirement since 401(k) withdrawals incur taxes but Roth IRA withdrawals don't. That gives you additional control over your tax rate in retirement, allowing you to minimize how much you pay the government.
Understanding the benefits and drawbacks of each retirement account can help you make the best decision for your future.