List<BusinessObject> or BusinessObjectCollection?

public class CollectionBase : IEnumerable

public class BusinessObjectCollection : CollectionBase

public class BusinessObjectCollection : List<BusinessObject>

var d = new Dictionary<string, int>
{
    {"hello", 0},
    {"the answer to life the universe and everything is:", 42}
};

class c1 : IEnumerable
{
    void Add(int x1, int x2, int x3)
    {
        //...
    }

    //...
}

var x = new c1
{
    {1,2,3},
    {4,5,6}
}

var x = new List<Customer>
{
    new Customer("Scott Wisniewski", "555-555-5555", "Seattle", "WA"),
    new Customer("John Doe", "555-555-1234", "Los Angeles", "CA"),
    new Customer("Michael Scott", "555-555-8769", "Scranton PA"),
    new Customer("Ali G", "", "Staines", "UK")
}

class CustomerList  : List<Customer>
{
    public void Add(string name, string phoneNumber, string city, string stateOrCountry)
    {
        Add(new Customer(name, phoneNumber, city, stateOrCounter));
    }
}

var customers = new CustomerList
{
    {"Scott Wisniewski", "555-555-5555", "Seattle", "WA"},
    {"John Doe", "555-555-1234", "Los Angeles", "CA"},
    {"Michael Scott", "555-555-8769", "Scranton PA"},
    {"Ali G", "", "Staines", "UK"}
}

public static int SomeCount(this IEnumerable<BusinessObject> someList)

public class BusinessObjectCollection : List<BusinessObject> {}

public IEnumerable<BusinessObject> GetBusinessObjects();

public OrderItemCollection : IEnumerable<OrderItem>
{
    private readonly List<OrderItem> _orderItems = new List<OrderItem>();

    void Add(OrderItem item)
    {
         _orderItems.Add(item)
    }

    //implement only the list members, which are required from your domain.
    //ie. sum items, calculate weight etc...

    private IEnumerator<string> Enumerator() {
        return _orderItems.GetEnumerator();
    }

    public IEnumerator<string> GetEnumerator() {
        return Enumerator();
    }
}

public MyTypeCollection : List<MyType>

using BusinessObjectCollection = List<BusinessObject>;

System.Collections.ObjectModel.Collection<BusinessObject>