Spark plugs

NGK BP7ES is my recommendation.

I use the Iridium equivalent to BP7ES, never had a plug foul in 10 years. 

Does electronic ignition make a difference? 

Analogue EI eg Boyer MK3 and MK4 in black box do not need resistance in plug, cap or HT leads.

Digital EI ie Boyer red or blue box need 5K ohms of resistance in plug, cap or HT leads. This is to supress EMF which can affect the internal chip and so timing. 

I have used the standard Champion plugs (N7YC) in my Commando for 32 years and never any issues. 

During this time I have used  a Mk 3 Boyer electronic ignition and moved to single carb conversion almost 20 years ago. 68 mpg and plugs always in excellent order.

Bear in mind that it is getting difficult to source non-resistor spark plugs. Only a problem for bikes with magnetos of course, not these new-fangled coil ignition machines. 

Modifying Resistor Plug to Non Resistor Plug - DIY

https://www.youtube.com/watch?v=5FOtJUbjpoo&t=2s