I use (and teach) a "normal stroke" for jumping. I believe it is more accurate, and enables you to do more with the cue ball - including aiming the shot, and applying jump draw, top and english. The "normal" jump stroke is more natural, and looks just like a normal jacked-up shot, only the cue ball gets airborn. In fact, jumping ~1/2 a ball about a diamond away, you can draw the ball a full table when jumping with your playing cue and using a "normal stroke" - which you can't do with the dart. Sidearm is an alternative, but IMO, is much harder to learn.
In the end, whether you use normal, sidearm or dart, is a function of what you need to accomplish and what your body can accomodate. Tall people can get away with the "normal" in more situations than short people...
As for jumping chalk, it is the same as a 1/2 ball jump. I often use a piece of chalk when instructing beginning jumpers so that balls don't go flying off the table everywhere. So 2 chalks is a full ball jump. The downside is when chalk bits go everywhere...
-td