When it comes to glow plugs, it is not a matter of saying "Brand X' is "better" than "Brand Y"

Of course, there are variations in quality between manufacturers. However, to say one brand is better than another is simplistic.

I like a lot of different plugs, and think the Novarossi range are excellent. Many have never heard of them.

O.S., by position of market dominance, are pretty much a default choice for many. They put out a quality product. To say they are the best in any given application is a matter of opinion. I don't use them personally, except for the "F" plug in O.S. and O.S. clone four strokes.

Like spark plugs .... Autolite Vs Champion; NGK Vs Denso Vs Bosch .... all are good, if used in the correct intended application. Then we get to types of spark plugs ,,, but that is an off topic discussion.