The default query form setting out-of-the-box is the expanded "standard" form. New with 10gR3, you also get the Query Builder form that allows non-technical users to build more advanced queries. Query Builder also includes some new advanced options for power users.
One thing you may want to do at some point is change the default query form view. Users can set their preferred query form view in their profile. Once a user sets this in the profile it will override anything you or your admin set as the system default.
To see where all this query form view decision making is happening we will take a quick peek at the "determine_search_form_type" dynamic html include:
Upon examination of this include you can see that you can use DefaultSearchFormType as a configuration variable in Admin Server or [install]/config/config.cfg to control the default query form view. Also note, they provide a variable to disable a particular query form view, DisabledSearchFormTypes.
Out-of-the-box, possible values we can set are "standard" which is the default, and "queryBuilder".