Hard one, some people cant hear det on teh electronic ones and some cant hear it on teh home made ones.....

I prefer the electronic ones for one simple reason....
Because we tune a lot of different cars, i find some pick up points are better than others for different engines, so i have the option to attatch 4 different pickups and swop between them on mine to filter out normal noise from knock...

I would say the normal type are best for the DIY enthusiast as:

There is, somewhere, a "How to build some" topic i recall, and if not, maybe there should be.
Hope this helps.