You have to consider the characteristics and costs of the various sensors as well as the available instrumentation. In addition, Thermocouples generally can measure temperatures over wide temperature ranges, inexpensively, and are very rugged, but they are not as accurate or stable as RTD's and thermistors. RTD's are stable and have a fairly wide temperature range, but are not as rugged and inexpensive as thermocouples. Since they require the use of electric current to make measurements, RTD's are subject to inaccuracies from self-heating. Thermistors tend to be more accurate than RTD's or thermocouples, but they have a much more limited temperature range. They are also subject to selfheating. Infrared Sensors can be used to measure temperatures higher than any of the other devices and do so without direct contact with the surfaces being measured. However, they are generally not as accurate and are sensitive to surface radiation efficiency (or more precisely, surface emissivity). Using fiber optic cables, they can measure surfaces that are not within a direct line of sight.
To select the optimal temperature measurement device for your application, you must first have an understanding of the differences between Thermocouple, RTDs and Thermistors.