I agree with Pokemario. In general, my advice would be to start with the character who you most enjoyed playing during the main campaign. Since Trespasser is new content, and it (hopefully) hasn't and won't be spoiled, you can experience the shock and surprise for the first time with your favorite Inquisitor.
Part of me wonders if your human Rift Mage isn't your favorite because you listed them first. With the Qunari being known enemies in Trespasser, your decision in Iron Bull's personal quest is sure to have some kind of context, which could be pretty interesting.
... if it was my choice I'd choose the 2nd play through as my 1st run.
^^ In the end, I'm going to have to agree with this.
If you play Trespasser with any character that didn't romance Solas first, then you'll already know the context of his return to the game revealed to you and it might spoil the romance-related surprise of seeing him again. Solas isn't my favorite romance, to be honest — so, I don't personally care about the potential romance stuff related to him that Trespasser might hold. That being said, if you really enjoyed the Solas romance, I think it would be more gratifying to see him return to your romanced Inquisitor first.
As for me? I'm going to start with my female Trevelyan who romanced Cullen. She's not only my favorite, but also my completionist who was friends with Solas.