As several people have mentioned, sound effects are most commonly in WAV format. Since you have to run many of them and they need to be synchronized with what you see, CPU usage is prioritized.
Music, on the other hand, since it's usually one or two simultaneous tracks, prioritizes file size, so compressed formats are common. And because most players won't notice a difference, lossy formats like MP3 and OGG are generally preferred.
MP3 used to be a proprietary format (I believe the license has changed since then), so depending on the engine you were using or if you were using libraries, OGG was often recommended. From a technical standpoint, there isn't usually enough difference to justify using one over the other. Some people prefer MP3 and will give you good reasons, others use OGG and will also give you good reasons. I'd say that, historically, MP3 is slightly more common than OGG.
Formats like FLAC aren't commonly used because they take up more space, and most players won't notice the difference.
The problem is that you're talking about creating a developer pack, NOT one for the end user, and that changes everything. Some developers prefer MP3, others prefer OGG, some want FLAC, and still others even WAV. Choosing one or the other will only cause you to lose parts of your potential audience, so it's best to offer it in several versions, and ideally, make your main version a lossless one. This way, each developer has the freedom to adapt the audio to their needs instead of forcing them to choose what you consider the most common format.