The most typical materials used in machine design are POM and different polyamide grades, such as PA6, PA66, and PA12. Other good options are from the polyester family: PBT and PET.
PP is an affordable commodity plastic, but in many cases, its versatile qualities might offer a valid option for applications that do not require high strength, stiffness or thermal resistance.
When mechanical requirements are limited to impact resistance and chemicals are not involved, amorphous plastics ABS, PC or PC/ABS can be the best choice.
Alloys of semi-crystalline and amorphous plastics, such as ABS/PA or PC/PBT, can be tailored in an attempt to combine the best qualities of both material groups (which includes the risk of combining the worst).
Technical does not automatically equal poor appearance. With proper design and appropriate tooling/process, the result can be visually very pleasing using semi-crystalline materials. Making amorphous materials withstand continuous load or chemicals is a harder task.