Welding probably causes more performance issues than pivotto because it’s handled by physics, setPrimaryPartCFrame and model:PivotTo achieve the same goal. The one difference is that SetPrimaryPartCFrame requires a primary part.
TL;DR - use PivotTo()!
Welding, obviously (if your model needs to be unanchored).
Keep in mind that welds are not physical constraints. PivotTo will likely perform calculations in the background to get the pivot offset which will take away from performance.