Looking to buy one Hard Drive which will work out of the box with windows and macOS as well. Nothing much to discuss more I think as I have no idea on what to buy 
for EX-FAT what will be the file size allowed ?It is a matter of in which file system the hard disk is formatted in, rather than which hard disk. As long as the hard disk is formatted in EX-FAT, both operating systems will be able to read/write from the same hard disk.
16 exabytesfor EX-FAT what will be the file size allowed ?
Go with the brand providing highest warrantyAny idea on which brand to go for in this case ? looking for a 2 TB version of external HDD.
To add on to this... and lowest price.Go with the brand providing highest warranty
what are the failure rates ?Go with the brand providing highest warranty