Due to the tax treatment of distributions, it would seem most logical to draw retirement money from regular taxable accounts first as well as use the required minimum distributions from accounts such as a 401(k), Roth 401(k), or traditional IRA. The last account to draw from would be a Roth IRA since it grows tax free, has no required minimum distribution, and is better for transferring assets to heirs.
This logic typically holds but it may be worth playing with the order in some cases. For example, if 401(k) withdrawals in excess of the required minimum distribution push you into a higher tax bracket, take out just enough to stay in a lower bracket and pull the rest from your Roth IRA because it is tax free. In other words, take your required minimum distributions, then take any additional amounts from taxable accounts and tax-deferred accounts but not allow these additional withdrawals push you into the next tax bracket. If you still find you are needing more retirement distributions, fall back on a Roth IRA. This will help keep your taxes down throughout retirement.