If you add fruit in secondary, you'll get more of a "fresh" fruit flavour. Primary some of the flavour will ferment out, and change (I have a mixed berry--which does contain blackberries--melomel almost ready for bottling. I got a flavour almost like red wine from the berries, although that may be due to the yeast choice as well). Personally, I say do both.
I do not use sulfites, and only occasionally pasturize (which could change the flavour slightly). Have you considered letting time do it's thing, with repeated cold crashings and rackings?
What yeast are you planning on using?
There is one secret ingredient that makes anything better......time.
Primary: Heather Tip Metheglyn
Secondary: Belgian Dubble Apple Ale; Raspberry Capsicumel; Rhubarb Wine; Pumpkin Wine
Tertiary (or higher): Oaked "Show" Mead
Drinking: New England Style Spiced Apfelwein; Whiskey Oaked Sour Apfelweizen