Why not use FAT32 for all drives for PC & Mac compatibility?
FAT32 has a file size limitation of 3GB maximum. If all your files are smaller than 3GB, then you could use this format. As hi-definition video files and compressed backup files get larger, the 3GB limitation may prove to be problematic for you. There are a number of other technical issues with FAT32 format but this is the primary objection.