does it matter which brand of air filter I buy for a chevy corsica?

i have recently bought a 85 pontiac 6000 they valve cover gaskets leaked bad that it smoked everywere. i replaced them it was a 2 day job if you've every owned one of these cars. it run good but had been sitting for 2 years. and as i drove it more it got to were it would'nt idle or had good power. so i decided to change the plugs and that was the answer it ran a alot better but two of them i could not get out they are stuck and they moved a little when i first tried to remove them and that was it they will not budge and from looking at the ones that came out all that oil dripping and burning on them wasn't good and very worn out. it has a 2.8 litre any suggestions would be helpful the two are against the firewall i don't have much room i have soaked them with pb blaster too no avail.