I have both - a fairly plain Justis and a fairly plain JB (I like plain). They both build high quality leather cases but I favor the JB. In fact I ordered my JB to make up for what I saw as deficiencies in the Justis. And it did make up for those deficiencies and I love it.
The Justis pockets, with the zippers on the side and the rigid tops to emboss designs on, don't hold a cue extender that I like to use and were hard to reach into to get stuff. JB let me specify larger pockets and top zippers.
As has been discussed a lot on here, the Justis interior doesn't protect as well as the JB. The JB interior holds the cues snugly with a lot of foam protection, the Justis lets them rattle around to some extent.
My JB holds a jump cue butt in the main compartment - John fashioned an insert to prevent it from falling down in the tube. This leaves more room in the pockets for accessory stuff, like the extender.
Although practical, I don't like rivets holding the case together. JB used thick stitching on mine.
Finally, the JB is less expensive.
Both JB and Justis put a lot of care into their product and are concerned that you are happy with it, but I think JB goes the extra mile in that regard. He made me an offer that I really couldn't believe. If I wasn't happy with the case he would start work on a new one and I could use the one he had sent and just send it back to him when the new one is done, no charge. I don't know if that's his standard policy or not but it kind of knocked me for a loop (I was very happy with the case he sent and didn't take advantage of this offer).
Justis makes a beautiful case and his decoration is flawless although limited in scope. From what I've seen, however, JB's team can do carving and dyeing that are worthy of being put into a museum and at a price that is very reasonable for what you're getting.
I think I saw a post that said Jack isn't taking orders for a number of months so he can clear out his backlog, but check that for yourself.