A word of caution here, and this is my opinion only. Others' may differ.
If you are going to be storing important data on the drive, I would suggest that you DO NOT use a "cross-platform" format scheme (i.e., one that is also readable on a PC).
Stick with HFS+ (which will limit you to use on the Mac only, unless you install some additional software on the Windows side).
The reason is that it's all too easy for the drive to become corrupted. I've read numerous cases of users with a cross-platform drive, who took it to the PC, and, POOF! -- the data was gone.
Again -- for storing important Mac files, use a Mac-formatted drive.
Get a SECOND DRIVE (or a large-capacity flash drive) to be cross-formatted. Fewer chances for disaster...
Again, this is my opinion only.