Note that even 100% JPGs lose a lot of color info so if you're going for quality, you do not want to use JPGs ever. PNGs for 8 bit files and TIFFs or OpenEXR for float should be your preferred formats.

Also there is no difference between JPGs, PNGs, TIFFs etc in terms of RAM usage. They all get converted to uncompressed formats on rendering and all take the same amount.