The non ventilated, if you construct it properly, would be much better performing than a ventilated. It will cost you more, but you probably know that.
The most important issue is to make sure the construction is 'breathable'. Do not use EPS, PUR, or PIR insulations... use softboard type with hydroscopic insulation such as rockwool.
I can refer you to a typical make up if you like.. its specific to a particular company (which i do not have any allegiance).. so id perfer to send you a PM about it rather than post it here.. .im not sure of the rules....