I have to say that I like them all. I have not actually had a chance to play any of them myself, but I have been in games alongside or DMed for many of them. I've seen Hunter, a couple Slayers, Knight, several Thieves, Mage, and Sentinel in action, and they all seem decent and pretty well optimized right out of the box, which is especially good for newer players.
The thing that strikes me the most about them is just how versatile they are. I find that it's easier to twist the fluff of the E-classes to suit concepts compared to the classic 4e classes. Maybe it's the simplified structure, maybe it's the decreased stat dependency in the builds, I don't know, but whatever it is, it really works.