Not really sure what the comparison is here.
Assuming that the brass and the loaded rounds are the same ammunition type, and assuming that the the factory rounds are boxer primed, then probably the factory rounds.
Why?
The brass will be reloadable and, you will be able to shoot some, confirm functionality in your rifle, and when you come to reload you will
know whether or not your loads compare to factory, or improve on it.
You can pull a couple of the bullets and experiment with different powder and primer combinations (especially given that "uncommon" is likely to mean that the OE powder and primers are no longer available).
You can dismantle a round and reassemble it without powder or primer. IDK if anyone else does this, but I always set my dies up by assembling an inert round. It gives me something I can use to confirm that my loaded ammo will feed, chamber and extract correctly. Since this round is "uncommon" the availability of a snapcap is likely dubious anyway.
You will be able to use the rifle immediately.
60 cases is more than enough to develop a load and assemble enough ammunition for a couple or three stalking outings.
So come on
@kenbro I think we deserve some more detail here! What rounds/cases are we talking about? Or is it purely hypothetical?
And since you've posed the question, what's your answer?