Parquet 4 eva
Csv is for arcane software or if you don’t know where it’s going.
Hdf5 is for Matlab interoperability
Otherwise I use parquet (orc could also work, but I never actually use it). Sometimes parquet has problems with Pandas or polars but I’ve always been able to fix it by using pyarrow
And now we have free threads so I can’t say at least you don’t have normal concurrency problems 🤣