Hi! The first mega pack is more focused to props and a lot of items (like consumables and so on). The modular structures are for indoor levels only in it. The second one is primarily focused to modular structures and many many small and large props. The modular structures in it are both for interiors and exteriors. It also has whole buildings, and is around 2.5 times bigger than the first one.
The both packs are unique and doesn't share any duplicates of the assets, and are compatible with any other of my PSX style packs.
Each pack has a list of contents as a demo download available. You can have a look, if you like.
Both packs are pretty neat. Whichever you'll choose, you'll be satisfied!