Vegeta because DB finished so he got a full writing. But Killua imo didn't leave some unaddressed writing... Kurapika yes, I think his revenge arc wasn't resolved and had yet to be more explored.
Killua made sense to me in a psychological controlling way... As if Illumi's last nail stuck in him and its release was (literally and figuratively) his true departure from the psychological disturbances attached to the twisted love of his family... Which also fits the Alluka arc, with him breaking free and freeing a sister from a situation of which he was kinda of brainwashed to take for granted... I don't see much potential for further expansion.
So Vegeta and Killua ... Vegeta may have more nuances, but some may argue Killua was kept more consistent, with Vegeta kind flip flopping