Preferred choice of opponent sensing

Electronics noob taking a crash course on my first sumo bot based on the Viper kit. Between Infrared and Ultrasonic range sensors, what have you guys found to work more effectively and more reliably?

Thanks

IR is fast enough if done right. Ultrasonic is generally considered too slow to use with sumo. Look at the sensors this guy is using… viewtopic.php?f=10&t=7385