Pro: Simple, stable, recognizable. Quadcopter technology is rapidly evolving so upgrades are plentiful and increase performance while getting cheaper all the time. Quadcopters usually have more power overall.
Against: Quadcopters are slowly losing credibility as being serious machines, they're considered toys by most people or at the very least consumer electronics. Heavier than their tricopter counterparts, so they need more power to achieve the same performance as their multicopter cousins with less motors.