Folded, most definitely.
This kind of discussions that are absolutely and utterly pointless, are the best discussions. Having folded or unfolded chips in front of me has no effect whatsoever on the decision of "to eat or not to eat," but I chose the unfolded because you don't need to crush it in pieces right after putting it in your mouth.
Unfolded! To be specific, it has to be McCoys - MAN CRISPS, Salt and vinegar. Nomnomnomnom
I actually prefer eating the folded chips over the flat chips in a bag, not sure why. I'll eat the entire bag, but I tend to pick out the folded ones first. I have no preference, they taste the same!