Ok so my warranty is expired just changed my oil. Now im changing my spark plugs but which ones should I get the Bosh 4+ platinum or the NGK iridium or whatever I already have in my 2003 bmw m3. I don't want to go to the dealer they jack up the price for everything made me pay 30$ for oil filter then found the same one at autozone for 6$. In your opinion should I stick with what spark plugs I have or switch to bosh?