Sorry Nikki but I'm going to say the complete opposite. I've never been a carto fan so this only goes for atomizers, but I've bought a lot of atomizers for my 510. The only ones that I've ever had any luck with have been genuine Joye. The eGo-C I just got has been really good and there are not knock offs for it (yet).
Basically I think it comes down to how you use the product. I've had Joye atties crap out after a couple of days. I've had generics do the same. I've also had both last for many weeks. One thing I have found is a dry atty won't last as long as a flooded atty. This hole thing reminds me when the first 510 knock off's came out. They looked like they had a washer in them just above the coil. Some people had good luck with them others didn't.
Personally I like the genuine Joye products and have had good luck with them.