Woundwort, Hazel, Cowslip, and the Threarah
This is kind of a battle royale, with every Chief Rabbit or leader serving as foil to every other rabbit-in-charge. To see how different these rabbits are at leading, you can imagine what one of them would do in another's situation. Put Woundwort in Cowslip's situation, and instead of staying around and letting humans kill them, Woundwort would fight and try to get away.
But don't start loving Woundwort yet. Because Woundwort is pretty terrible as a bully towards his rabbits. So if we put Woundwort in Cowslip's place, he would save the rabbits from the humans and then start killing rabbits for disobeying his rules. At least the Threarah doesn't kill other rabbits, right?
Well, the Threarah doesn't kill other rabbits (that we know of), but he doesn't do a very good job of listening to other rabbits, either. And when it comes down to it, he's just as worried about his power and authority as Woundwort. Except instead of beating up other rabbits, the Threarah has "wily courtesy" according to Hazel—he manipulates rabbits to get his way (7.7).
Only Hazel brings all these good qualities together while minimizing the bad: he'll do whatever it takes to save the warren, but he won't turn into a monster to do so. And he knows that the important thing is that the rabbits survive, not that his political authority survives.
Bigwig vs. Fiver
Bigwig is an action hero, and Fiver is the inaction hero. There's a pretty handy paragraph that neatly captures this distinction between the two: "In front of him stood Bigwig, sodden wet, undaunted, single-minded—the very picture of decision. At his shoulder was Fiver, silent and twitching" (8.25). A lot of the book is about how Bigwig and the other rabbits come to see that Fiver has his own talents to offer. Even if those talents aren't as obvious as Bigwig's physical skills. In order to survive, the warren is going to need both the action hero Bigwig and the guide Fiver.