I personally prefer H difficulty for the campaign.
Mainly since compared to N difficulty the eleutheroi actually is aggressive at times, and they can end up sieging cities from time to time.
Another thing is that diplomacy is a bit easier to handle then on VH difficulty.

I don't always like the feeling of being the big bad faction that everyone is after, even when I am just a small empire. :)

I find it very frustrating to get overwhelmed early on by playing smaller factions, since I take my time and don't expand to fast.

I haven't played on VH campaign much, as I found H to be what suits for me.
Again this is just my personal opinion, and I hope it was helpful. :)