What are the respective benefits of each?
SharePoint Stack Exchange is a question and answer site for SharePoint enthusiasts. It only takes a minute to sign up.Sign up to join this community
Resources in Style Library will most likely send the correct caching headers.
There were issues in 2007, here is a good rundown.
Another option is to deploy this to your _LAYOUTS folder.
As djeeg point out, Style Library has issues (304's due to incorrect max-age). I am not sure this is fixed (it would surprise me!).
Another plus for storing in a virtual directory is that you can use them across web applications, since they reside in the SharePoint root folder. This ofcourse can also be a weakness if you need permissions or versioning, so as usually when we are talking SharePoint, the answer is "it depends" :-)