TubeNet

Which one would be better for a conn 3j cc tuba, which one would work for all types of playing?

It depends on what kind of sound you want. Personally, I think the Jim Self (JS) is easier to drive over a wide range of music. JS is deeper cup and less rounded on the inner rim, I think. So, even though the internal diameter is nearly the same on the two MPs, the rim on the JS makes it feel like a smaller I.D. and easier to manage for me.

I posted some additional comments about the Bobo with a recording of me blasting away in the background here (last post in the topic):
viewtopic.php?f=2&t=30840&p=270920

If I had to pick only one to keep, it would be the JS.

I finally settled on the JS for all around use. I tried a bunch and it worked better on my little 184 than anything else I tried. I was shocked when it also worked the best on the VMI 3301. I don't have a clue about a larger horn, but it bested a full range of PT's, Shilke's and assorted others for me.

I played a Yamaha Jim Self mouthpiece for about 6 months. Besides for the obvious reason (I'm a moron) I have no good reason why I didn't keep it. I loved the way the mouthpiece felt and the horn sounded great using it.