Didn't you look at them in Google?
The Sharp IR rangefinder sensor is in-accurate and is used in cheap robots. If many readings are taken and averaged then the result is fairly accurate.
Ultrasonic rangefinders are as acccurate as the frequency of their quartz-crystal clock since then measure how long it takes for a reflection to be returned.
The power of the beam determines the longest range.
The material that causes the reflection also determines the range since a matt black object does not reflect IR well and an absorptive soft object does not reflect ultrasonics well.