While it's not simple to really say which one is "better", each clearly has their own strong suits, and have crafted their styles to reflect the strengths accordingly.
Ina's accuracy and intense levels of detail, particularly in the clothes and anatomy of her works make them seem almost like fine-art portraits, while Sana's dynamic expressions and bright colors really make her pieces pop to seem more lively. In a way, their artwork is inherently indicative of their personalities irl.
I'd love to see more Art from Sana on-stream or at least post-stream before further speculation, since her art is still new. Meanwhile, we've seen Ina's technique improve over the year, along with her speed and confidence on-stream in that same amount of time. I'd love to see the two together do more art, but Sana still seems to be keeping her powerlevel hidden besides official Holoworks, and her own portrait.
All in all, there's two absolutely phenomenal artists in EN right now, and whichever one is "better" is up to personal preference more than anything else.
TL;DR: It's fucking Art, and they're both phenomenal
