It’s difficult to give a definitive answer without seeing the data. If you need to read the data repeatedly, in parts or lookup specific elements then sqlite or a database (in memory/on disk) would be better than files. But if you’re just loading different datasets and can’t prepare a database/memory store in advance, files would be the better option.
Qt doesn’t really mind how you have the data stored. If you’re using the model views you’ll need to implement an interface (and some kind of caching) since the views require a lot of data lookups for individual cells (usually very inefficient to hit a database for that).
If you’re passing data in/out of a process then an external data store then you have a choice between piping the data or using an external data store (including a a file). Pipes make more sense when streaming the data (i.e. you have a live output) and don’t need to store the result. If you’re storing the data and only need access to the finished result, I’d put it in a store/file and just notify the main process to read it once you’re done.
Does that make sense? If you have more details of the data I’m happy to go into it further.