When I was younger I had a mix of just about everything-- my normal setup in my 20s had Zildjian, Sabian, Paiste, and Istanbul and even a Wuhan china for a while. By the time I hit my 40s I was all-Zildjian and when I experimented with other brands I'd get a small set of Paistes or Bosphorus or whatever. For the last two years it's been 100% Paiste. I still keep a Zildjian Overhammered Bounce in my collection just because I really like Paul Francis, but now that he's making his own stuff I'll almost certainly sell it.
For me, it's kinda easier to choose all cymbals from the same brand, and often even from within the same line. That's where I think Paiste really shines. Everything's certainly interchangeable, but it's also easy to create a full set out of 2002s, Modern Essentials, Signatures, Masters without dipping into other product lines. To me, that's a selling point.