In the world of 3D scanning, the right scanner depends on the application, but also on the main goal of the people who will use it. Each method has its benefits but also its trade-offs. This paper aims at helping individuals and companies select the type of 3D scanner that is right for them. The market nowadays is full of different types of products, different system categories, as well as, often, several different manufacturers for each category. This can make the selection of a 3D scanner both difficult and confusing. To make things simpler, we categorized 3D scanners according to one of their main features: the positioning method they use. The measuring arm, the tracked 3D scanner, the structured light, and the portable 3D scanner categories will be investigated. More specifically, the two main positioning methods used by portable 3D scanners will be discussed: positioning through targets, and positioning through natural features. A third method called hybrid consists in combining the two. The positioning method is defined as the way a system captures the 3D space and then aligns the data collected during the scanning phase. 3D scanners are used for pipeline fitness-for-service evaluation in replacement of conventional methods such as pit gauge and ultrasound probes. Corrosion and mechanical damage can now be characterized with very high accuracy and repeatability. Each scanner category has been tested for corrosion assessment on a pipeline. We will see how they perform against each other and the importance of a proper positioning method.