Zram offers way more flexibility and versatility compared to ImDisk.
Zram can be used for swap space or as a general-purpose RAM disk. Unlike a traditional RAM drive, Zram can compress data using a nice hand full of algorithms, notably Zstd; allowing it to store more information within the same RAM capacity leading to faster I/O and efficient memory usage with minimal CPU usage; & LZO-RLE; offering the fastest compression and decompression speeds leading to faster data swapping between compressed and uncompressed states, potentially improving overall system performance. Also, ImDisk afaik only offers NTFS compression for RAM drives which is… well… pretty damn slow for this particular use comparatively.
Additionally, Zram persistence can be configured with writeback devices. ImDisk typically doesn’t offer persistence.
ramdrive.sys isn’t even worth talking about, it never had any kind of compression let alone anything else I mentioned previously.