The Halal and Kosher slaughter methods might be the most humane ...
There's a secret video of the realities of slaughterhouses at this Guardian link:
It shows that the notion that we consume meat from 'humanely' killed animals is a delusion. Stunning is a very crude, imprecise, and messy business, which results in some (many?) animals being slaughtered whilst actually conscious.
Here's the words that I've come across from one poster on a discussion forum:
"I advocate what amounts to the halal approach (a sharp knife) ... if the blood is loosed from an artery not near to any sensitive parts of the body, ... there's no indication at all of the usual fear reactions of such animals at all. Consciousness is lost before the animal dies, and, it seems, with as little pain or trauma as possible (bearing in mind taking any life prematurely will cause some trauma, even if only physical)."
The notion that halal slaughter is barbaric compared to what we civilised westerners do is simply another instance of surreptitious Islamophobia - which, as Sayeeda Warsi (a leading Tory, no less) has pointed out, is now so widespread that it has actually become socially acceptable within polite society.