I've tried the K&N replacement filter for the Picanto and I've noticed improvements in fuel consumption not to mention a noticeable acceleration improvement. The cost of the K&N filter actually pays of when you bring back your car to the service center.
The exact part number of the K&N Drop-in filter for the Kia Picanto that I used is 33-2930 and you can find more details at the K&N website.