Which Document Carries More Weight?

I'm going to go with the first document - the photocopy of the page from the baptisimal register.  My reason is that while the photocopy itself might be new, it is showing a document that would have been created near the time of the event.  The second, "certified" copy is something that has been created entirely in the current time-frame (since it was sealed by the current parish priest) meaning it is farther away from the time of the event.  Also, since it is a newly created record, there is more of a possibily that it could be altered by the priest to fit what the requestor needed it to say.

I have to agree with Diana. The first copy, although uncertified, is of a register page. This makes the certificate suspect since it appears someone would have copied it from an older register which could introduce error. Or, as Diana stated, the current parish priest could have a bias to change the document. Although the photocopy could have been altered, without further information, I would weight it as the more reliable of the two and continue searching for more documents, especially the original register.

Somewhat echoing the previous posters, I would give the uncertified photocopy more weight, based on the information we've been given.  I would also emphasize that neither document is necessarily to be trusted and I agree that the search for more evidence should continue.

The problem I have with the photocopy is that we don't know who made it.  If it was obtained as the result of a direct request of the parish clerk (or whoever -- the specifics here are beyond my experience) then I'd be more willing to trust it.  If it just appeared out of the blue, we can't even be sure the photocopied document is legitimate.

Let me be the odd one out here. To prove my case in court, I would want to convince the judge about the provenance of my information (chain of custody). For the uncertified photocopy, it is uncertain where it came from. As a genealogist, I may recognize it has hallmarks of authenticity, but I cannot expect a judge to know that. I do not expect a judge to take my word for it, so I would want to submit evidence that has a proven origin. I would rather submit the certificate signed by a priest than an uncertified photocopy, even though as a genealogist I would prefer to photocopy (substitute for original record) to the certificate (derivative). 

Alternatively, I could submit the photocopy and sollicit the expert testimony of a forensic genealogist to explain why that is more trustworthy than the certified certificate.

The baptismal register would be the more reliable document as it's closer in time to the event and presumably recorded by someone with firsthand knowledge of the event.  But Yvette makes an excellent observation that the provenance of the birth register would probably be an issue.  I think I'd try to get a copy of the baptismal record that had been certified as a "true and authentic copy" by the authority in control of those records.