Obviously selecting the right buildpack is critical in order to make secure, performant, and resilient applications. Heroku seems to work with the dev community to create and share buildpacks. A side effect is that there may not be a single, 'obvious' choice for a given tech stack.
Random example (R)
If we wish to use an R buildpack, a quick google show this popular buildpack is out of date and no longer supported, but we can easily find these three (just examples) here, here, and here
Another random example (cairo)
The cairo buildpack - googling shows numerous in the top results, it's not clear which to use out of, say, the top four on google here, here, here (this one clearly states deprecated, so we can rule that out), and here
Question
What are the main criteria against which we should assess heroku buildpack when faced with >1 that look like they will do the job?