Final answer:
A developer should create a Summary report to display the number of open positions by department to hiring managers. This type of report efficiently groups and aggregates data, which is ideal for the purpose of understanding recruitment needs. Other types of reports like tabular, pivot, or analytic snapshot may not be as appropriate for this specific task.
Step-by-step explanation:
To show hiring managers the number of positions grouped by department, the type of report a developer should create is a Summary report. This kind of report allows aggregation of data, such as counting the number of positions, and then groups these counts by a specified field, in this case, by each department. It's more effective than a tabular report, which simply lists all the records without grouping or summarizing them. A pivot table is also useful for summarizing data, but it's more complex and typically used for more detailed data analysis that may involve multiple dimensions and aggregations. An analytic snapshot, on the other hand, is designed to capture historical data at specific intervals, which doesn't appear necessary for the stated requirement.
Regarding the best way to group data, it often depends on the context and the specific questions that need to be answered. Grouping data by department here is useful to aid hiring managers in understanding recruitment needs and workforce distribution. One could also consider grouping the data by position level or types if the focus was on the structure of career progression or diversity of roles within departments.