DEPENDS...
IF I have a frame thats the right size and Im comfy on and it has what I need for angles /attachment points I would rather upgrade.
upgrading is more fun, unless your doing a brand new everything and doing a self build.
I like to upgrade cuz I can procure and install parts that no Factory ready bike can or will offer.
But If You have a quirkey little road bike and want to make it into a touring machine then upgrading wont work...
"John"