Now I'm pretty sure you will just rip me apart for this as always, but I guess you could say the Ta'veren are a mixed of the four temperments. Obviously theyre all choleric, being leaders of some kind, but Rand is the melancolic, Matt is the sanguine, and Perrin is the phlegmatic.
Or theyre the 3 times of general male personallities. The Firebrand (Matt being the joker and general) The Thinker (Perrin for his slow thought and more attention to detail) and The Savior/Leader (Rand for obvious reasons.Kinda like the soldier who throws himself on a grenade to save his buddies or goes running across a battelefield to help someone aka LT. Spears from Band of Brothers.)
Any way thats my theory, and I'm sure its off by a lot but just throwing it out there. Maybe itll lead to someone coming up with something better.