Well, from what caught my eye. The Audi S5 top model seats have a massage function for one. Audi grade of seat leather feels better than what Genesis uses. The Audi seats seems to have more padding as well. The tech is superior with a very nice display in the instrument cluster. The 20in wheel choice looks better to me personally as do the overall styling of the S5.
The price would be the only reason why I would not buy a fully optioned out S5 over a fully optioned out G70 sport. I sat in both the G70 and S5 when I was just "window" shopping in my local dealerships, but never drove neither. So I do not how one drives over the other. I also checked out some newer Mercedes and even a Dodge Hellcat. Overall, I like how the Audi and Mercedes cars feel in the driver seat, but not the price tags.
Remember, this is only my personal opinion.
Admit it, if the fully optioned S5 cost the same as the fully optioned out G70 you will be tempted as well to rock the Audi badge.