Which of these 2 companies produced better revolvers?

[hrt4me]

Santa Barbara (Spain) or Centaur (Belgium)?

 

[Long Johns Wolf]

How do you define "better"?
If you refer to the steel used both makers used harder steel compared to Italian makers incl. 2nd and 3rd gen Colts.
You are talking about handling? There are the shooters prefering the grip geometry of the Centaure which replicates the Colt 1860 Army (usually the ones with the mid to bigger size hands) over the ones of the Santa Barbara (usually the ones with the smaller hands).
You talk about pointability? Hands down the Centaure.
If you prefer a stronger, closed frame percussion revolver? Go for the Santa.
You wish to shoot longer shooting sessions without cleaning? The Centaure shines again.
There is one important difference to be considered, however: For the making of the Santa the historical measurements of the chambers' dia (.446") and rifling groove dia (.451") were replicated which has an impact on accuracy.
Regarding the latter, this is where the makers of the Centaure stepped away from the orginal. The Centaure was designed to be as accurate as possible. Hence, chamber dia and rifling groove dia are both the same (.446") like you find in a modern target revolver.
My 2 €-Cents.
Long Johns Wolf

 

[hrt4me]

Thank you, @Long Johns Wolf !
I am also familiar with your website, which has been helpful as well.

 

[hrt4me]

@Long Johns Wolf, which round ball diameter do you prefer in the Centaure?

 

[Long Johns Wolf]

.451" is the recommended ball size for the Centaure.
Long Johns Wolf

 

[hrt4me]

@Long Johns Wolf, are parts from any other manufacturers compatible with Centaure? I have to replace a missing 1860 barrel stud for the loading lever latch...

 

[Long Johns Wolf]

Sorry, had never to replace one.
A smith should be able to make one from scratch or modify an existing one from an Italian 1860 ...
Long Johns Wolf