These guys speak from experience, many of us have been down that road...
If you truly only want swing jazz (or whatever) you can look at what come in each pack and decide, but most of us ended up hearing something someone else did, and realized we would have liked to have that option.. the larger packs are the better deal as opposed to eventually buying a bunch of realtracks.

The megapak does seem to include a number of additional jazz styles and realtracks compared to pro.

I do not work here, but the benefits are still awesome
Make your sound your own!