Keep in mind the most popular is not always the best.

In terms of type being used, number wise the most popular is probably stock.

Do you mean the most popular "upgrade"?

It's not scientific but you could post polls on all the Jeep forums you can find. The problem with polls are, well, many. One problem is, if the majority of participants are "mod happy", let's say (and I'll bet they are) a lot will say whatever mod they have done is the best simply because they have done it. Fred Blackstone has written a couple of essays on the phenomena. I can tell you around my 'hood the TFI up grade is the most popular ignition mod (besides the ECM bypass). I believe it delivers the biggest bang for the buck so to speak. I know of several others that have done it in my Club but not one that has gone HEI. There may be one or two that have used Aftermarket ignition modules. I like the stock one, (it has never let me down and if it does I can replace it for $15).
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