Jack is quite different to me than Jim. I actually prefer Jack because of its heavy char taste and flavorings, and I think JB White feels younger and has thin legs for a Bourbon. JB Black is definitely a step better and I'll buy it when cornered by lesser stuff, but too sweet to be a regular pour. I'm not a fan of Knob either which is their older aged stuff.
I do like Bookers immensly though-which stands to be their Super Premium.