List or BusinessObjectCollection?

Question

Prior to C# generics, everyone would code collections for their business objects by creating a collection base that implemented IEnumerable

IE:

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Answer 1

You can use both. For laziness - I mean productivity - List is a very useful class, it's also "comprehensive" and frankly full of YANGNI members. Coupled with the sensible argument / recommendation put forward by the MSDN article already linked about exposing List as a public member, I prefer the "third" way:

Personally I use the decorator pattern to expose only what I need from List i.e:

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

    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 Enumerator() {
        return _orderItems.GetEnumerator();
    }

    public IEnumerator GetEnumerator() {
        return Enumerator();
    }    
}

Further still I'd probably abstract OrderItemCollection into IOrderItemCollection so I can swap my implementation of IOrderItemCollection over in the future in (I may prefer to use a different inner enumerable object such as Collection or more likley for perf use a Key Value Pair collection or Set.