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Are you talking about a OS X boot drive or just a shared data drive? I'm not sure NTFS or exFAT can even be used as a boot format for OS X.

I used exFAT for a data drive, but even then it had problems so I don't recommend it any more. I couldn't find any OS X nor Windows backup software that would recognize exFAT drives. Occasionally Windows would think the drive was corrupt and would not provide write access until a chkdsk was performed. Chkdsk would then find zero errors, and write access would be restored. This cycle happened about once a week for a few months and then mysteriously stopped.

If it's a boot drive, I'd format for HFS+ Journaled. Windows will have read access when you install the boot camp drivers. If you really need write access too you can install third party software.

If it's a data drive, I'd format for NTFS if Windows is your main OS or HFS+ Journaled if OS X is your main OS. The "other" OS will have read access and you can install third party software for write access.
 
I'd rather go for HFS+ (Mac's default) and use a Linux partition to share it with Windows than having my drive in NTFS. One of the worst filesystems ever. DUH
 
Thanks guys, appreciate the advice.

The HDD will be just for data and I will make a copy of it as a backup. It will probably have just photos on it and maybe a Time Machine backup.

I will leave the stock HDD as it is. Long term I would like a server of sorts to house all of my HDD's. I use both OSX and Win, but won't be using Win much more as I want to switch to Mac.
 
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