Choosing between immutable objects and structs for value objects

Question

How do you choose between implementing a value object (the canonical example being an address) as an immutable object or a struct?

Are there performance, semantic or

Answer 1

As a rule of thumb a struct size should not exceed 16 bytes, otherwise passing it between methods may become more expensive that passing object references, which are just 4 bytes (on a 32-bit machine) long.

Another concern is a default constructor. A struct always has a default (parameterless and public) constructor, otherwise the statements like

T[] array = new T[10]; // array with 10 values

would not work.

Additionally it's courteous for structs to overwrite the == and the != operators and to implement the IEquatable interface.