get NGK coppers for ~$2.50 apiece. the 4 bangers come with ngk coppers stock and they are easy to replace. change them once a year for best performance.

platinums are crap, they are designed for longevity not performance. iridiums combine performance and longevity and are best for cars that the plugs are hard to replace in like the V6. since you have a inline 4 those plugs are easy to replace so why not change them once a year with ngk coppers.