First choice: original.
Second choice: period correct.
Third choice: modern upgrade.
Depends on the bike as found (how much is original and overall condition of frame), also depends if it is common bike, versus something special. 99% of what I get are what I would call good vintage but common bikes.
I also let economics enter into the plan, in particular, resale value. I try not to overbuild a bike, even a "keeper". (I have tended to replace keepers as I find "better" keepers. The longest I have had any of my current keepers is one year.
+1 I commonly change chain rings to make the bike a better match for my motor. And I really prefer aero brake levers.