I've got an 04 civic, so my stock spark plugs are good, but I was wondering what spark plug is considered to be one of the best performance-wise? Iridium NGX? Other?

 

dont bother. there is really no performance gain in going to a different plug. as long as yours are in good shape, just let them be. when you do replace them, I recommend either bosch platinums, platinum +2, or NGK platinums. ive had bad experience with/heard from quite a few others whove had bad experience with the Bosch platinum +4s. oh, and if you drive pretty hard, get the plugs one heat range cooler than stock.