What is the difference(s) between ultrasonic sensors- such as the SRF04, 05 and 08, and the sharp IR sensors ?
How far your robot needs to see is the primary difference. The SRF04 can pick out an obstacle from 3 inches to 10 feet (6 cm to 3 m), a Polaroid (Senscomp) can range 2 feet to 35 feet (0.6 m to 10.7 m) and the Maxbotix LV-EZ0 ranges from 6 inches to 21 feet (15 cm to 6.4 m). The Sharp GP2D12 ranges 4" to 30" (10 cm to 80 cm) the GP2Y0A02YK ranges 8" to 60" (20 cm to 150 cm) with others varying near those.
If the robot is outside, it might be possible for the sun to "swamp" the Sharp sensors, basically over-running their detectors so that they are unusable, though I haven't seen this yet. I've had a couple Sharp sensors outside for tests and not had any detection problems unless the sensor was directly aimed at the sun, though others may vary. Not too many overbearing 40 kHz sound sources to swamp out sonars in most environments.
Detection width is also a difference, with the sonars usually having a wide area detection pattern, sort of a fan in front of the device. The Sharp sensors are much more narrow in their detection.
The final difference would be the interface to the micro being used. SRF04s need a trigger and a timer/counter pin, as do the Polaroids, and the Maxbotix sonar can use a single timer/counter, or an analog pin, or serial. TheSharps that do range are primarily analog, though there are some that are proximity, detecting a at a set range for use with a regular IO pin.
i will probably use ultrasound for my first bot.
rapid electronics only sell the SRF 04 and 08, and techsupplies sells the SRF05.
the 08 is expensive and has an extra light sensor, but the 05 seems to be the most widely used.