I always used NGK Iridium because I believe that if you have the money to get the most quality part at the time and dont mind spending it, do it. For piece of mind mostly. I always use ngk iridium and have never had any issues. My F23 felt a little peppier when I used them but my old plugs were.... well, old. I used them in my H23 and I still use them in my f20b. Thats just my opinion on things anyway. Seals and gaskets for me are ALWAYS OEM. Suspension and stuff is usually Moog. I always try to use brand name parts.