Sorry for the reflexive dickishness. It's a chronic condition here.
Because it's such a relative discussion, I think you have to stress and confront the most basic meanings of the word "leader" as opposed to diplomat, benevolent dictator, administrator, etc.
Regarding the "safety" aspect, I think it's a wash on the issue considering there have been no invasions of Korea during his reign: meanwhile, the country was ravaged and brutalized for centuries prior and had half of its population killed by the US during the Korean War.
From what I've read, Un is definitely more intelligent than Trump, but that really is hardly a compliment. I regard Trump as being fairly indisputably less intelligent--and most shockingly less willing and/or able to learn and humble himself to new information--than the average college graduate. Truthfully, even most of his supporters here seem to be more intelligent than the man himself. Un is multi-lingual, extremely well-educated, and from what I have read has demonstrated his being fairly capable in domestic policy, as evidenced by the fact that DRKA isn't as famished and impoverished as it was during the late years of Jong Il.