air filter

Hi. 2 months ago I bought Opel Corsa C 1,7 CDTI 2005 and I´d like to start modding it. The first mod on my list would be an air filter. I´ve read a couple of threads and still don't know what to do half of them say that it's better just to buy a high flow panel filter (Pipercross or K&N) and the...