Best file system for both Windows/ Mac

I have a portable hard drive for school, and occasionally I need to use Macs.  I know typically USB flash drives come formatted so they work cross-platform, and I don't know why my hard drive couldn't have come like that.

Without partitioning the drive, what file system should I use so that both OSs can read/ write?

unfortunately, fat32. It FAILS HARD but it will do the trick

I considered FAT32, but I work with animation/ large video files, for 4 GB limit really is a hard fail.  I just ended up going with NTFS for now and screwing the idea of using it on a Mac.