I think with rifts you mean FATEs? As the term rift is pretty much a RIFT specific term?

They're mainly done for ATMA farming these days, not so much for leveling purposes anymore. For leveling dungeons, challenge logs, hunting logs and questing tends to be fastest. Only in higher level content there's often sufficient players FATEing to make it worth it.

Random queues can be joined as groups for the higher level roulettes. The low level roulette however is as of yet still a solo player signup.