Which function is best for joining two different models in Siemens NX?

The function that is best for joining two different models in Siemens NX is the Boolean Union. This operation combines two or more solid bodies into a single solid by merging their geometries. When you perform a Boolean Union, the resulting model retains the volume and shape created by the intersecting bodies, effectively treating them as one continuous solid.

This approach is particularly advantageous when you need to create complex geometries by integrating simpler shapes. Boolean operations maintain the integrity of the models while allowing for modifications, which is essential in design workflows where the interaction between various components is critical.

In contrast, the other options serve different purposes. Assembly Join is used for positioning components in an assembly context, while Merge Models is typically not a common function in the same sense as Boolean operations. Link Assemblies involves referencing external components without merging them into a single body. Each of these functions has its specific application but does not provide the same capabilities for creating a unified solid shape as the Boolean Union does.