I have done both, and prefer the spiral. In fact, I have the old "glass pack" style inserts just sitting in the shop right now.
I did notice that there was more deep bass tone at an idle with the glass pack units, but the spiral baffles allow for a wicked tight sounding rip when you nail it.
I imagine on a high reving small block, it would be even more wicked sounding.
The spiral baffles are going to last longer and will be easier to service as the glass packs will eventually rust in place and become "one" with the pipe.
You can get with C3Sharktank Scott for your supply of the JCL baffles.