I found this on the Developer Hub:
Performance note: When the
Parentof an object is set, Roblox begins listening to a variety of different property changes for replication, rendering and physics. Therefore, it is recommended to set the Parent property last when creating new objects. As such, you should avoid using the second argument (parent) of this function. You can read this thread on the developer forum for more information.
Which refers to a new thread on this forum about the parent argument of Instance.new. Long story short, it is best practice to set the parent after all properties of a new object are set. This is the best option in terms of performance.