The Yamaha amps have no fan noise and are more efficient. They use a variable power supply that continuously changes the rail voltage to what is needed to reduce heat radically. According to Yamaha, they have the efficiency of class D amplifiers, but yet use standard AB class output stages. The increased efficiency is especially useful for home users that want high power without having to add in more dedicated circuits.
The Yamaha amps are not exactly compared to the Behringer. The Behringer is made for a more versatile range of uses, as it is 2 Ohm stable, and the Yamaha is intended for 4 Ohm use. But as the Yamahas have no fan noise, they are more suited out of the box for home use, and they look better, if that is an issue. Also, the rack mount wings are removable from the Yamahas, allowing them to match regular consumer gear even more closely.
The Yamaha amps I recommend are the P2500S, P3500S, P5000S and P7000S. They all use the same topology; just pick the one that fits the power range you need. The P5000S and P7000S are slightly different from the other three. These two last, higher powered models use switch mode power supplies in order to remain low in weight, while the lower powered three units use standard power supplies.
-Chris