I was just wondering, which decoder, IonCube or Zend Optimizer offers the best performance?
I guess the question is... what exactly are you trying to achieve?
My own tests have always shown ionCube offers better performance (and, in my opinion, is an all round better solution). I'm not aware of any recent benchmarks, but, you might be interested in this: http://www.olate.co.uk/development/benchmarks.php - lots of food for thought
Based on benchmark testing ionCube encoded files can provide faster execution times on PHP 5 under realistic test conditions.
You can find more technical benchmarks stuff here: http://www.ioncube.com/benchmarks.php
In any case, choose what meets your needs.