What air filter should I buy?...

I only want a panel filter as I think this is best, any makes people seem to have success with for a 2004 STI JDM?

 

K&N or Green.

 

non stardard fillters can ruin your MAF. Go OE

 

K&N are fine.

The other statement above is not true for Newages, assuming you stick to a decent make.

 

My99/00 cars then I would agree on part, but only oiled filters or induction kits, this is an my04 car and the maf is different.
OP, sti panel filter, it's a service item and should be changed every 20k and not cheap but it's very good
The other thing is with these reusable filters like k&n is that you can never clean them 100% and they will retain dirt no matter what you do, so even with these I would be replacing them at 30-40k with a new one.

Tony

 

I,m running a K+N on my 05 JDM STI. I,ve used it on my previous 4 imprezas over 11 years. Cleaned it a few times but never oiled it. No problems so far. Steve.