SHARP IR RANGE FINDER or Sonar for stair edge decetion?

[tc66tc]

Hey guys, Im look to use either IR of sonar for edge detection.  I am looking to keep the robot from falling off a table or avoid stairs.  The distance (from surface to lower surface) will range from half an inch to 6 inches.  Which one of these would be best for this?  I am new to robotics and this site is incredible.  I used the search function and didnt find anything so figured I would start a new topic.

Thanks
Tc

[Trumpkin]

Sharp IR, it's about half the price.