Taff & Froggy, my two cents worth..
DONT touch a champion plug, NGK irridiums I have found to be crap, mainly from my experiences with an overly rich KX125, I have not used Densos in my bike - my old man is a (particularly fastidious) mechanic, and I recall few fond reports of Denso plugs.
All said, with my KX, I changed from the irridiums (and I brought plenty of them @approx A$24.00 p/plug) and changed to the Gold and plaitinum tip plugs at approx A$14.00 ea. and never fouled one or burned it out after that! in fact I gave 5 or 6 new plugs away when i sold my KX, and am still finding the odd one about the house wrapped in bubble rap, as thats how I liked to transport them in my tool kit.
I'd stay with NGK's for sure, but I'd look at the Gold or Plaitinum versions.
Azza.