There are three thought processes on this, whether in the world of Dragon Age or the real world.
The first option is that a strong ally is one that is self-sufficient, independent and domestically stable makes the best ally because you need not worry about them and therefore do not have to micromanage their internal affairs. This alliance works best when both nations share the same interests. The second option is that having weaker allies who are dependent on you for continued stability/support are the best allies to have, because they are not in a position to betray you or back out of commitments. The third option is the combination of the two, a strong-ish, somewhat stable nation that is not utterly dependent but still concludes that the continuation of the alliance is in its best security interests.
I applaud BioWare for how they handled the situation with the Orlesian leadership, and I think the "best choice" depends on your characters and your World State. For me, my Warden had no hate for Orlais but also had the bigger view in mind...ultimately, political issues like "The Game", the Assembly in Orzammar, Loghain's treason, etc. are all smaller issues compared with the Blight or the Breach. My Inquisitor also has a similar view. While he wants the situation in Orlais to be under control and to reduce any marginalization to specific groups, but ultimately he doesn't care what the best, mot optimal outcome for Orlais is. He cares what is best for the Inquisition and the people of Thedas.
So for me, having Gaspard, Celene and Briala rule together is the best option because it allows Orlais to end the Civil War and add Gaspard to the ruling council, which strengthens domestic stability, political leadership and legitimacy. However, they all still kinda hate each other and it can be assumed that somewhere down the line they will try to assassinate each other again. This keeps them on their guard, and they cling to the Inquisition alliance and support more than they might without the threat of the others. The perfect middle ground between dependence and outright independence.