How do you boost lower level characters?

Other posters have commented that 4 warriors and a Shammy is the best farming group power wise for end game, with 1 Warrior and 3 Mages at 2nd. I can tell you from experience with a mixed comp, it can be very complicated because the classes all have different spells with different cast times. However, what you lose in kill speed you make up for in utility. For instance, with my WPMLS I can reset a dungeon and start again in 1 min with all hearths on CD. Make my Mage leader, port the mage to Org, log out the other 4 toons to the character selection screen, reset dungeon, log 4 toons back in, they reset at the beginning of the instance, and walk outside and summon the mage back with my lock.