This is a discussion that has bothered me for a long time. There are debates and studies which try to suggest that one or another of "first to file" (FTF) or "first to invent" (FTI) is better for one or another type of inventor (small inventors, etc).
A recent article in IP Osgoode demonstrates the problem. In referencing a study the article suggests, "The study finds that the shift to FTF resulted in a reduction in the number of patents granted to individual Canadian inventors and small businesses". This is a study based on the Canadian experience having made the switch to FTF in 1989, with the USA switch coming into force in 2013.
The assumption of the article, and most of the debaters, is that if some patents are good, more are better. The fact that the number of patents granted went down after a change should not be presumed to be a bad thing, when in fact patents not being granted may just as easily be a good thing for innovation.
Governments granting statutory monopolies need to be understood as a government intervention in the marketplace for a specific public policy purpose (See: Statutory knowledge monopolies and supply management). The success of the patent system must then be measured against that public policy purpose, not measured based on number of patents granted or some other nonsensical measure.
Innovations which are strong in utility, novelty, and unobviousness should be encouraged, and in these relatively rare cases I believe it is justified for the government to interfere with the free market and grant statutory monopolies to the innovator. The innovator should then be free to decide how they wish to benefit from that reward, thus making the monopoly able to be sold (IE: a form of intangible property) is also appropriate.
Innovations which have weak or fail to demonstrate utility, novelty and unobviousness should not be granted a monopoly. The interference by government with the free market ends up being a disincentive for innovation. Individuals and companies who independently develop a product may then find some undeserving statutory monopoly holding company is able to block and/or "tax" (monopoly rents, royalties) their independent innovation.
This brings me back to the FTF vs FTI question. If two innovators independently come up with the same inventive idea, such that the differences between FTF vs FTI matter, I believe neither is deserving of a statutory monopoly. It seems obvious to me that if FTF vs FTI matters, then the innovation is weak in novelty and/or unobviousness.
What I believe would be appropriate is internationally harmonize on FTF for the simplicity of paperwork, but have the type of documentation previously used in FTI jurisdictions to change ownership of the statutory monopoly to instead invalidate the statutory monopoly. We currently allow far too little prior knowledge to be used as prior art in determining novelty of innovations, so expanding this would be beneficial to all innovators.