IP Office mode is easier to use.
Intuity mode allows users to modify their mailbox more extensively ie up to 4 greetings, ability to differentiate between call types ie internal, external, busy, no reply and play different messages.
But in saying this flexibility comes at a cost, as most users find it more difficult than ipo mode.
It is also more secure as it has password policies.
IPO mode allows easy setup with groups
cheers