...or provide a way to customize which item in the enumeration is chosen by default.

The first item ("always") in the enumeration is selected by default. A careless or lazy reporter will thus erroneously imply that he/she has tried to reproduce the problem and can do so at will. A more appropriate default would be "have not tried". I've reordered the supplied values in my installation so that "have not tried" is the default, but I think Mantis should be shipped that way.