The Pocketbook 360 is the best 5" device, I agree with you, but the "overall best" reader currently on the market is, IMHO, the BeBook Neo / Onyx Book 60. It has an excellent screen, a Wacom touch screen which doesn't affect image quality, and excellent firmware, with such features as annotation and dictionary lookup (neither of which the iRex 800 has). 6" is an excellent compromise between size and portability.
The iLiad, as mentioned by the original poster, is a very strange candidate for anyone's idea of the "best" reader. It takes an eternity to boot, has a very short battery life, is much too big and bulky to easily carry around, and has not been supported by its manufacturer for some considerable time.