I would've said that Syndra's ambition for power is her main driving feature, just tied in with her desire to never be shackled down. I feel like her ambition comes out stronger since the not submitting thing is a result of that ambition though. Course that's just one way of looking at it.
Azir could be an ambitious ruler, a tyrannical ruler, a ruthless ruler, a compassionate ruler, etc. I figure ambitious works considering his goal as a ruler is to bring his nation back to its former glory, which is a pretty tall task. His ambition is empire sized.
And with Garen, I feel like justice is more of the goal he sets out, not a feature of his personallity, if that makes sense. He could pursue justice in a variety of ways, but through courage and determination is how he does it.
I feel like I'm looking more at personallity traits specifically though, so my perceptions might be a bit skewed.
This is why champions have three pillars that speak to their personallity; one generally isn't enough to encompass an individual.