Avenged sevenfold would be toward the bottom of the pile when it would come to technical metal. They are merely a radio band, dont let your emotion for a band determine what would be considered "hard" to play.

If you want some true, and quite obnoxious to be frank, technical metal; you need to look at bands such as Cannibal Corpse, Decapitated, Nile, etc.

But thats what is nice about guitar, it has a lot of different aspects and directions where someone could go. As per your example, Dragonforce is good in their own realm, but you also have the style of that Andy McKee fellow. And of course you have your classical guitarist. And then you have the insane improv abilities of the Jazz guys.

I guarantee you, there wouldnt ever a consensus amongst a group of random guitarist on what the hardest song to play would be.