I intend to use various external hard drives with my new mini... Time Machine
Well, the Time Machine drive will have to be on HFS+.
For everything else exFAT will do nicely.
I'm not keen on exFAT. It doesn't have redundancy like FAT32.
OS X will write to NTFS via a terminal command.
Sorry whatdo you mean by 'redundancy'?
Yeah I've been using it for years and it's been absolutely flawless. There are some free options too but they aren't as stable. So for the sake of £6ish (at 50% off) to me it's not worth worrying about but if you want to try an alternative:
http://i.vishalagarwal.com/post/30387627819/ntfs-write-on-lion-or-mountain-lion