Equivalent Classes

Format 1 - Array Format

This is better because the StaffClass contains all the information about the staff member including the "id".

public class AllTheStaff 
{ 
    public System.Collections.Generic.List<StaffClass> staff { get; set; } 
} 

public class StaffClass 
{ 
    public int id { get; set; } 
    public string firstName { get; set; } 
    public string lastName { get; set; } 
} 

If you need to convert a List into a Dictionary you can use this:

System.Collections.Generic.Dictionary<string, StaffClass> StaffDictionary; 
StaffDictionary = AllTheStaff.StaffClass.ToDictionary(staff => staff.id); 

Format 2 - Dynamic Keys

public class AllTheStaff 
{ 
    public System.Collections.Generic.Dictionary<string, StaffClass> StaffDictionary { get; set; } 
} 

public class StaffClass 
{ 
    public string firstName { get; set; } 
    public string lastName { get; set; } 
}