Start from the form, not the process
Form-verification parts and fixture components are usually moderate in size and dominated by flat and curved surfaces, where structural proportion, colour and how they read on the line matter. FDM with PLA expresses them well and makes geometry and dimensions easy to revise.
Small structural parts and detail-dense prototypes go the other way: small scale, dense surface detail, and sometimes a surface left unfinished. DLP with rigid photopolymer resin presents that level of detail better.
Then the use and operating conditions
Pieces kept indoors mainly to be looked at differ from those repeatedly handled, loaded, or brought into contact with tools. The latter must be confirmed against load, dimensional requirements and operating conditions, and usually call for a separate review of material and structure rather than a default process.
Where size, colour or support geometry is concerned, the notes on a product page are only a starting point and need to be confirmed through inquiry.
How quantity and finishing shift the choice
One-offs and batches lead to different arrangements. Our own equipment covers samples and small batches; complex modelling or specialist finishes are assessed separately. The larger the quantity, the earlier inspection method and consistency requirements need to be settled.
Surface condition is a frequent point of divergence. Whether the part stays in its printed colour for you to finish, or arrives with a finished appearance, needs to be stated when we talk.
A practical order to decide in
Describe the form and scale, then the use and operating conditions, then quantity and the finish you expect. Once those four are clear, the process usually follows as a conclusion rather than needing to be decided up front.