In terms of what? Vocal talent? Dancing skills? Variety show speaking skills?
In my opinion, Jessica has the upper hand. She has a very well-trained voice with a nice, clear tone, soft vibrato, and solid vocal control. Jessica was also originally supposed to be a lead dancer. Her movements are very fluid yet strong, and very expressive. On Strong Heart, she was voted second best speaker, 5% behind fellow member Sooyoung.
Hyuna's very talented as well, but very far from what Jessica's abilities. But they're both very different, so it depends.
I enjoyed Flower Power and I look forward to the rest of the album.