Pjurcia,
That is an excellent question!
My answer is that what makes a cue break well and what makes a cue jump well are opposites, so I recommend both. Keep in mind that we have just come out with "The Break Cue", which is a low deflection or low cue ball squirt break cue.
Here's the thing. Most current break jump cues use a one piece phenolic tip ferrule combo, or at least a traditional ferrule with a phenolic tip. These will usually jump very well, and they break really strong IF you hit it VERY WELL.
We found that most players don't hit it VERY WELL as often as they think. With a high deflection cue shaft, if you miss the center of the cue ball, the high squirt pushes the cue ball to the side causing a less than full on hit on the front ball. You lose quite a bit of energy when you don't hit the front ball square. With a low deflection break cue, like ours, even when you miss the center of the cue ball a little, you still hit the front ball more full or square.
The result is not necessarily a bigger break, but certainly a more consistent one!
Unfortunately, in a normal configuration, a low deflection cue shaft simply does not jump that well. You can jump with it if you have a very hard tip, but it is not as easy as with a jump cue.
So, thats my take on it.
Use a Low Deflection break cue to break with, and then use a Jump cue to jump with.
Thanks
Royce Bunnell
www.obcues.com