I have only a limited anecdote to offer, but here it is: My first foray into E-6 processing was with a Paterson Chrome-6 3-bath kit. About three months after I first opened it, one of the developers (I've forgotten if it was the first or the color) had turned completely black, so I didn't dare use it. My second E-6 kit was a Kodak 6-bath kit. I've had it for about a year and it still works. (That said, I've not done any precision color tests; it could be the color I get is slightly off now. As I scan my E-6 film a slight color shift isn't a big deal to me, though.)
That said, there is a drawback to the Kodak kit: It's much harder to use. The Paterson kit involved a process that wasn't much more complex than C-41, but doubling the number of baths for the Kodak kit makes it all much more tedious.