Aesthetically, which so far is the only department I can talk about, the only thing I like more than the A45s is its carbon ceramic 380mm disc option, though they could've gone the extra mile of adding an 8 piston caliper. They could've also upgraded the rear brakes with carbon ceramics, but not only did they not, they also kept same old 310's that look tiny compared to the fronts. Audi cheaped out there. As for everything else, including interior, I find the A45s is miles ahead, while performance remains to be seen. I'm sure carwow will arrange a drag race sooner or later.
Power wise, there really isn't much room for the RS3, as it can't be near RS4 territory and as I've already said, I'm glad MB's pecking order isn't that strict. So the best they could've done was just catch up. Impressive they have allegedly pulled that off without a power increase, but let me take this with a grain of salt until that drag race actually takes place.
I also wanna see how it sounds, as it's been rumored it won't sound nearly as good as pre-opf generations. Should still sound better than the A45s, but that also remains to be seen. I don't like judging from things I'm not yet aware of.