Never had a problem with NGK on any bike, car, outboard motor, lawnmower ...
Occasionally had them foul, but that's down to poor maintenance, bad tuning or ignition problems, not the plug's fault.
I don't recall ever having a dead one out of the box. I've not found the heat ranges difficult to live with either.
I reckon I'll stick with them mainly because I'm familiar with the numbering system. If I look at an NGK, I know exactly what it is from the number. But with a Champion, KLG, AC Delco, etc. I'm lost. The numbering system may as well be in heiroglyphics for all it tells me. I know you can look up a reference table in the shop when buying them, but I always feel a little uneasy doing that (if the correct NGK isn't available). I have no reason to think there's anything wrong with non-NGK plugs, it's simply my own lack of experience with them.
Not had any problem with NGK caps either. Only time I've ever had to replace one was because it was busted in a crash.
Cheers,
Cam