Collectible figures arrive finished: no gluing, no painting faces with a three-hair brush. The spread of scales is wider than people expect, from small 1:64 sets used to populate a scene alongside car models up to large 1:6 figures with textile kit and jointed limbs. Subjects take in film, gaming and animated universes as well as military figures in specific uniforms.
Because those groups have almost nothing in common beyond being ready-made, the notes below sort them out and explain which one suits what you already own.
Small 1:64 figures are bought in sets and exist to populate a scene — people in working and everyday poses give a car model context and scale. Larger collectible figures from film, gaming and animated subjects are standalone pieces with carefully finished faces and poses. Military figures in 1:6 form a third group: textile uniform, separate equipment and an articulated body, so they can be posed into a specific situation. The fourth is robots and mechanical characters from fantastical universes.
If the point is to bring a scene of models to life, the scale of everything else decides for you — a figure half a step too large spoils the whole tableau. For a standalone piece on a shelf, pick a larger scale where the face and the equipment can be seen. 1:6 is the most demanding on space and rewards you by behaving like a small scene in itself.
A static figure in a relaxed stance fits into a case among other exhibits. An action pose seizes attention but needs space and a reason around it; a running figure in the middle of an empty shelf looks awkward. Jointed 1:6 figures let you change the pose later, which is worth paying for.
Film and gaming characters are collected in series and their value lies in completeness. Military figures make sense in the context of a period and a unit instead. A little of everything is the fastest route to a case with no story in it.
If you would rather build and paint a figure yourself, the widest choice of scales is in model figures, with large subjects in 1:6 figures. Mechanical characters as kits come from Gundam and Gunpla and fantastical themes from the sci-fi and fantasy branch. Other ready-built subjects are in collectors models.