For aircraft:

Formal: fuselage or wing span aligned with centerline of plinth. Suitable for museums and collectors alike.

Oblique: aircraft placed at an angle to the plinth. Suitable for collectors especially for dioramas or more causal setting.

No base (basic collector option only): for the collector who prefers to either mount his own model or wants to display in a glass cabinet. Risk of damaging the model when picked up is much higher.

Ships

Waterline: many kits come as waterline and are suitable for dioramas

Full hull: Suitable for larger scales and submarines