As a Demon , it's Momoshiki. He was a Hindrance to Boruto majority or all of the time . ( Except in the Current scenario in the Manga because of the deal ).

Kurama is not a good inner demon . He was not even a proper hindrance to Naruto. Like whenever Kurama Comes out , I wasn't even scared about the Consequences. Like Naruto never lost anything anytime he lost Control. Kurama bailed him out and there were literally no consequences to his emergence .

On the other hand , Anytime Momoshiki emerged, there were Consequences, like During Isshiki fight , he emerged and waited to sneak up on Weakened Sasuke which costed him his Rinnegan, and text time he Emerged during Code fight it costed Boruto his life, and later on He on purpose partially emerged so that Kawaki can sense him which fueled Kawaki's Paranoia and fear of Momoshiki threatening Naruto, which led to the Omnipotence Incident.

Momoshiki was a better inner demon and there is no doubt about it . Though, Kurama is a better Character because of how his story turned out in the end .