There were quite a few there that I liked - the wedding preparation and celebration was nice and different, I had to laugh at the Death Star reference in the King of the Mountain questline.
However, for a truly "favourite" quest or questline it would have to be something I'd like to do again. And even hacking the mainframe - and the followup - is not something I'm really looking forward to doing again.
Note: You are given the 'hacking' tool.
No, my favourite is an old world quest - newly designed with the Cataclysmic overhaul of the world. This one is available for Alliance in Northwatch hold (and there is a daily in Tol Barad). Blowing up boats just does not get old. I could do that all day!
Favourite quest: Run out the Guns!