I've had goo experiences with hedders but mostly bad. Stock exhaust manifolds are good if you get the right ones. I'm building my own hedders for my current project: a 401 Buick Nailhead in a 51 gmc pickup truck. But the truck is far from stock, having a jag XJ6 front suspension that buick motor and well, my own design frame.
Anyway, equal length, the correct diameter, smooth flowing tubes with enough spacing for the spark plugs, routed away from all the bumps ie: steering column, rack, starter, block fenderwells and frame rails, i'll write you all about my masochistic design and fabrication. If I'm really smart I'll take pictures.
Here's a tip:
Use oem exhaust donuts between the collector and the rest of the system in place of the flat p.o.s. gaskets