Official comment
Conditions to help the decision:
1) If you're never going to connect it to a player directly, but plan on using both OS's, use exFAT.
2) If you're going to connect it to a player directly and want to use the drive with both OS's, use FAT32.
3) If you're going to connect it to a player directly and only want to use it with a Mac, use HFS+.
FYI: GUID drives work for general use, just not for firmware updates.