Already a few times I have seen questions being closed because people were asking "What's the best Ruby library for doing XYZ?". I see the point that such a question, in general, may lead to endless discussions. However there are many cases where this is not the case.
Example: Best Ruby library for Excel files
Having dealt with such libraries big time, I know that the spreadsheet gem is with no doubt the best cross-platform gem when you need many features. win32ole is certainly the best choice if you want to integrate with MS Office on the Windows platform.
After all it can be a big time saver knowing which library to choose for what.
BTW, here is a counter example, asked by myself, that has not been closed:
So maybe instead of closing questions like this, one might suggest: hey, can you rephrase your question to point out what kind of use case your interested in.