It depends on who you ask. Ask a Ford dealer if Chevy is better. Ask Pepsi if Coke is better.
In general, all manufacturers are making a version of several models. Each has it's ups and downs. Joye, SLB, JSB, Boge, etc have bad lots of components from time to time. To say one is better or worse than another is to open up to an infinite range of criteria. Is this opinion based on vapor production, taste, component life, price, appearance, availability, size, variety, or any of a billion other factors.
Bear in mind that each vendor sends specifications to the manufacturer as to what they want in their end product. Some just ask for a generic lot, others ask for certain modifications. Janty, for example, has Joye manufacture their components to a specific level. According to Janty, they have each of their eGo
batteries coated with a specific paint process to minimize or eliminate paint peeling. Volcano and Revolver send specific information to their manufacturers to make their products more unique.
I don't like certain models from certain manufacturers because they don't perform as I would like them to. That doesn't mean that it's a bad product. Someone else might love the heck out of them. It also doesn't mean that all of that manufacturers products suck.
Bottom line, if you try a certain make and model and find it to be all that you wanted it to be, then
buy it. If not, then don't. "Genuine" only matters if you want it to. Everything is only as good as it's warranty and the customer service level of it's retailer.