I've used the Mopar versions, Purolator versions, Fram versions, and now Wix/NAPA versions all in my 3.6. The Mopars end up always being wavy. I feel like they are 1-2mm too tall which crunches them once you screw the oil cap in. The Purolators were fine and look identical to the Mopars and are sometimes wavy too. I didn't like the Fram's only because they're tough to remove from the cap and half of the time the spring in the cap pops out with them which is a total PITA. Otherwise the Fram construction looks like Hengst and is really solid which I prefer. The Wix filters are never wavy, fit great, and I've yet to find any pleat separation that some have previously seen. And the price is generally $2-2.50 cheaper than the Mopars. I'm using up my stash of Wixs currently and probably will re-purchase them or the Frams. Never tried the K&Ns.