Am I better off filing as head of household or as a qualifying widow(er)?

The tax rates for qualified widows or widowers are the same as for couples filing a joint return and are lower than the tax rates for a head of household.  So if you are eligible to use the qualifying widow(er) status, you should do so.  However, you should ensure that you actually qualify to use this status, which is generally only available if you have qualifying children, and then only for the two tax years AFTER the death of your spouse.  In the tax year of the death of your spouse, you can still file a joint return.  Use the IRS Interactive Tax Assistant to determine the best filing status for which your qualify.