title: Should we extend Comparer<T> or implement IComparer<T>
body: <p>What is the best practice in C# starting from version 4.0 when writing a comparer class :</p>
  
  <p>a. Should we inherit from Comparer abstract class ? or</p>
  
  <p>b. Should we implement IComparer interface.</p>
  
  <p>What are the pros and cons?</p>