If you can afford the overall costs of the WRX, then go with the WRX.
Why?
I think if you drive them both it'll be as clear as night and day.
Imo it's not what you get with the RS, it's what you don't get.
(And what you'll wish you had got, otherwise!)
That's a heavy, awd car and with 170hp it's not exactly nimble.
My 2wd 2009 Accord coupe has a fairly anemic 190hp, and it's clearly an Accord, not a race car.
Clearly, 170hp in the awd Impreza platform is a mutt, pickup-wise...
As a DD the RS certainly more placid than a WRX, and since it's not forced-induction, it's obviously not as much fun.
Since both cars are physically identical, imo it's the fun quotient of the WRX that makes it the clear winner.