Should You Save Vidar or Turn Him In?
Save entity:vidar. Side with him at the climax of Spread Your Wings, kill the Crow leader Self and the Crows, and keep your hands free of the assassination work that comes with the other path. The catch, and there is a real one, is that Vidar is not the innocent he plays. But the choice to protect him keeps you in control of your own story instead of running contracts for a murder cult, and that is the better outcome for most players.
Here is the full picture of both paths so you can decide with your eyes open.
The choice
Spread Your Wings builds to a single decision: protect Vidar from the Crows, or hand him over to them. The Crows are the Children of Morrigan, and their leader, Self, wants Vidar badly enough to recruit you in the process. Whatever you pick determines how the rest of the questline plays out and what you walk away with.
Side with Vidar
Choosing to protect Vidar puts you in a fight against the Crows. You kill the Crow leader Self and the Crows alongside him, which is the harder road in the moment but keeps you out of their organization entirely.
The quest then advances to A Crow Left of a Murder. From there you can keep working with Vidar to dismantle the Crows' grip on Kamelot and Avalon, pulling apart the network you just struck at, or you can part ways with him and walk your own road. Either way, you have broken the cult's hold rather than joined it.
If you are not confident in your character's combat, the fight against Self and the Crows is the part to prepare for. A build that can handle a group of enemies, rather than one carefully chosen duel, will get you through it cleanly.
Turn in Vidar
Handing Vidar to the Crows takes the questline in the opposite direction. Vidar is taken away, and Self initiates you as a Hatchling. That initiation comes with a Crow armor set, a tangible reward you do not get on the other path, and it folds you into the Children of Morrigan.
From there you run assassination contracts. The Crows mark targets they judge to be destabilizing the region, and you are the one sent to remove them. This is the path for a player roleplaying a killer-for-hire or anyone who wants the Crow armor and the contract work that comes with it. It trades your independence for membership in the cult and a steady supply of people to kill on their say-so.
The twist that should shape your choice
Before you decide that turning Vidar in is the cynical-but-clean option, know what the questline reveals later. Sirja exposes Vidar as a Children of Morrigan operative himself, one who ran a rival cell. He was not a victim of the Crows. He was a competitor inside the same organization, and he was using you the whole time to wipe out his competition and seize control of it.
That reframes everything. Side with Vidar and you are helping one Crow faction destroy another, doing the dirty work of a man who set you up to be his weapon. Turn him in and you hand him to his rivals and take his place in their ranks. Neither side is clean. There is no choice here that leaves you allied with honest people, because there are no honest people in this story; there are only two flavors of the same cult.
The verdict
Save Vidar anyway. Even knowing he played you, siding with him is the path that keeps you out of the Children of Morrigan's chain of command and ends with the cult's grip weakened rather than reinforced. You spend the rest of the questline tearing down the Crows from the outside, on your own terms, instead of taking contracts from the inside. You give up the Crow armor set, and you take the harder fight against Self, but you keep your independence and you leave Avalon with one less murder cult holding power.
Turn Vidar in only if you are deliberately playing the villain, want the Crow armor, and like the idea of running assassination contracts as a member of the cult. It is a legitimate roleplay, and the rewards are real. For most characters, though, the cleaner ending is the one where you refuse to join them.
For how this decision fits into the wider web of Avalon's branching choices, see the choices and endings hub. For where Spread Your Wings sits in the overall quest order, see the walkthrough.