deadtotheworld22:
In terms of specifics, I'd perhaps recommend either Hunter or Vampire, but I'm happy to give Werewolf or Mage a try. Changeling tends to be a very different game from the others and it's a lot harder to crossover (at least in tone, as well as some mechanics).
Having run massive, sprawling crossover LARPS, I've found that Changeling, Werewolf, Mage, and Hunter tend to crossover well, with Hunter and Werewolf occasionally having problems, and Mage crossing over the easiest
for the Mages (it's hard for the non-Mages to keep up though). Vampire fits the least with
all of them (Vampires are simply monsters, there is no easy way to reconcile that for most non-Vamp groups).
But as deadtotheworld22 I think is getting at, the genres, the themes, and scope of those different "lines" are vastly different. It's easiest to run them separately with the occasional "crossover event", or crossed-over character, who understands to temper themselves to the setting they are crossing into.
The hardest part of running multiple threads, that is multiple ongoing separate "campaign lines", is keeping them temporally lined up. Vamps can easily skip days and weeks, where Changelings and Werewolves are slogging through it day by day trying to deal with small individual problems (frex). And that's the hardest part, it's also a bit of a job to keep it all juggling together, though some GMs can handle that with ease and others find it hard to make sure everyone is updated on concurrent events (just something to think about).
My advice? Pick a game you want to run, and if you want to allow in 'non-standard' characters, then do so, but make their themes, scope, and conventions fit the Primary Campaign type.
My preference is Changeling the Lost, but dark fairy tales are my jam. But I'm equally happy playing Vampire, Werewolf, or Mage. I've had lesser experiences with Hunter, but that was down to the ST and us Players ahve radically ideas of the genre, the ST thought we be playing Big Damn Heroes facing down the vastly superior monsters, where we Players thought we were mere mortals fighting the last good fight to make the world slightly better, to whit we schemed, planned, and engaged with an over-abundance of caution, and in the end the expectation clashes caused the games to fold.