A umber of factors come into play when it comes to choosing an infrared camera: durability, ease of operation, temperature range, detector size, lens angle, sensitivity, as well as voice annotation and reporting capabilities. Another very important consideration is the work environment.
It is the latter that is often not taken into account but should be at the top of the list of factors, when shopping around for an infrared camera. Voice annotation comes in handy in regards to workflow and safety, since thermal imagers are designed for single-hand operation.
Infrared Cameras - Characteristics
If the camera is sensitive enough, it will provide clearer images and show the slightest differences in temperature (you will know with more precision how bad the leaking is). With a large enough detector - which means more pixels - you will either get more information at the same distance, or the same amount of data from further away. A wider lens is exactly what you need when scanning walls or floors - it will let you work close to these surfaces and still collect a lot of temperature data.
As you can see, choosing an infrared camera is pretty straightforward: with your needs in mind, as well as the characteristics of your work environment, you will make the right choice.