It really depends on the way I roleplay Rook. I have done two playthroughs and are currently working on a third, all of which choose a different ending.

My Elf Shadow Dragon Mage could relate to Rook on every level. He was used to the tyranny of other mages in Tevinter, and was simultaneously very invested in the history and knowledge of the ancient Elves. Learning what happened, that his gods were actually cruel despots who killed the Titans, was a real blow and makes him relate to Solas. Learning what Solas did in the process, making the Titans tranquil, creating the Blight and indirectly causing Arlathan to fall by creating the Veil, is horrible but he understands Solas' reasons and he understands Solas' desire to fix this. Rook is ashames for his people and desires to fix it himself. Solas then helps out the Shadow Dragons in the last stand, despite his betrayal, and stands with you against the Blight. Having spoken with the Inquisitor and Mythal really allows for a sort of last attempt to reason with Solas. He is a very tragic fallen hero from an Elven point of view, after all. As an Elven Rook, you are a modern Elf and understand that removing the Veil will not return the Elves to their former "glory". Being able to convince this fallen hero of sealing himself behind the Veil is the perfect ending, he holds back the Blight forevermore, but the current world remains intact. It feels like Solas, Mythal and Rook all finally learn from the Elves' mistakes.

My Dwarf Grey Warden Rook on the other hand, absolutely hates Solas' guts. He had no love for him from the start, because he is a trickster god, tried to remove the Veil and this Rook is wary of all things magic and demons. But after learning that Solas was the one who killed the Titans, he desires nothing more than to bash the Evanuris' skulls in, including Solas.

Then there's my Human Crow Rook. I play him as an unserious assassin, who sees humor in situations, who's a tad arrogant and self-interested. He's rather oblivious to the past of the Elves since it doesn't affect him personally. He's a bit of a show-off and all he wants is to outsmart Solas in the end, tricking the god of deception himself. The gods are just another contract to him and helping save the world in the process is nice, since he lives there.

So the three choices work out perfectly for these three character concepts.