I remain undecided...
I, too, have yet to make a final decision...
Bass-line -- win for Psy. Stands out more clearly/feels more distinct in the mix. Both songs feature repetition here. Content-wise, they are simply too different in style to remove personal preference from the equation. (victory based on technicality)
Vocals/melodic content -- win for Hyuna. Vocal performance is a head above Psy, with better annunciation to boot. 'nuff said.
Harmonics/integration -- win for Psy. The overall melodic nature of
Ice Cream tends to make up for short-comings, but the existing harmony is less complex that
Gangnam Style. Additionally, the bass and harmony in
GS blends better (i.e. -> do not drown each other out; cooperate well enough)
Artistic Expression -- win for Hyuna. [I feel that Psy is shouting his ideas, but still lacks the emotions expected from the lyrics (contempt or sarcastic ridicule). On the other hand, Hyuna sells it well with a pleasantly seductive emotional emphasis throughout the song, which exceptionally complements the "milkshake-brings-boys-to-yard" theme.
... I guess I give my vote to Hyuna, because I more quickly become tired of
Gangnam Style... Plus she's sexy.