Which Spark plug is good

[cemery]

I changed my mcd onroad rally cars Carburetor. My new carb. is walbro 813 HP. I am using in CY 26 cc engine. and sam 21 pipe
NGK CR 7 HIX and CR 8 HIX
iridium plugs are ofering but which is good I didnt decide

 

[Bigger the Better]

I have always used the CMR7H plugs and never have had a fouled plug. Iradium plugs are higher and more prone to breakage on roll overs.