Thanks for the answers!
Can you tell me which is the main and most important factor that defines the cue's hit...
LOL I think you got your answer already just based on how varied the responses have been. People will disagree over the extent to which each one of these factors has a bearing on hit, but in general, will agree that these factors are:
-Primary materials (shaft materials, forearm material, ferrules, joints, shaft inserts)
-Shaft construction (maple dowel, flat lamination, radial lamination, other variations such as predators' hollow portion, OB's unique process)
-Joint (As has already been documented in this thread, primarily wood to wood vs. piloted stainless steel, but also variations such as wood pilots, the lambros joint, etc.)
-Tips (hardness, laminated vs. not laminated, number of layers, material [which animal the leather came from, phenolic, composites, etc.], weather or not it has been soaked in dairy [not joking - look up milk dud tips])
-Taper (pro v. euro/conical, length of taper, unique tapers [e.g. Southwest's compound taper])
-Also weight and balance point make a difference, although I categorize this more as "feel" rather than hit - although others will argue otherwise and/or argue if there is even a difference
Personally I will echo the earlier post that I can feel the difference between piloted stainless steel and wood to wood joints, although some say that there is little difference. As far as construction, with the advents in technology and the mastery of cuemakers, no joint will cause significant mechanical problems (some people have problems with wood to wood pins destroying the wooden shaft threads and some have problems with metal pilots getting stuck - I blame this on the owners rather than the joints/pins).
I will go out on a limb and say that one of the easiest things to notice is the affect that the tip has on hit - in my experience almost everyone can definitively tell, even very new players. The taper has a very profound impact on hit as well, but conversely I find that most people do not actively notice a shaft's/cue's taper or attribute their preference for a shaft/cue to the taper.
I'm sure I've missed something and many will agree/disagree but either way I hope this helps you! I agree with whoever said it earlier that your best bet is to get exposure to as many different kinds of cues as possible to form your own opinion. Even on this board of experienced players, you can see how much we disagree, so it really is up to you to define your own definition of hit/feel.