Zak'kash knows what he wants and where he's going, he's got the martial skills to physically protect her and while he's a bit awkward, he's not a block of wood emotionally either. He'd make a solid choice, he's confident and mature enough to be someone she can depend on. The downside is that he's going to be going into combat and he might die.
Kagara is kind and clever, has a cat, and makes her laugh. He has no real combat skills and no goals or confidence. But he's clearly willing to learn to provide for the cat as best he can. He'd probably give her a festival full of laughs if he didn't continue to fall all over himself. Long term, he's less likely to die, maybe, but she might end up having to mother him along.
Namaji herself doesn't seem to have a real preference, but she also is offloading the burden of disappointing one of the boys onto you. So either too kindhearted or a bit wishy-washy? Long term, I feel like Zak'kash would fit that better, and she could let him show that softer side better. But I also feel like Kagara would work, and maybe the easier rapport they seem to have coupled with the greater responsibility she would probably have in that relationship due to his lack of confidence would steady her as well?
Also, Zak'ash might be sad not to be chosen, but I bet there are a bunch of girls who'd be willing to fix that for him, due to his status. Also, since he has a goal, he would get over it pretty well, I feel. Kagara would probably fold like a sad wet tissue, but Zak'kash implies he's smart so he too might have others eyeing him as well.
All in all, Blizzard, I hate that you made me think this hard about this. Good job. Great quest.