I am no engineer, but these ships must be built with some "give," like a skyscraper.
Jiminy'sGirl SHOULD have been an engineer. Ships do indeed have some "give" ... in fact it's quite a significant amount. Naval Architects refer to this as "hog" and "sag" and it's absolutely essential for structural integrity. Imagine a situation where two wave crests are about one ship length apart. The ship is essentially supported at the two ends while the middle of the ship dangles above the trough between those two crests. The ship needs to sag a bit rather than breaking in half.
Although critical for structural integrity, this is mostly a second order effect for ship motions and is not significant except for the most severe ship motions. So, there is not a significant difference in the rotational motions (pitch and roll) between the bow and stern (so PP brentm77 is also correct in his statement). My more complete discussion of ship motion (in which I specifically noted that I was ignoring the flex in the ship) can be found at this location:
http://disboards.com/showpost.php?p=47077663&postcount=6
One additional factor that I did not previously address but posters have experienced is something called "slamming" in which the bow of the ship ploughs into the on-coming wave face. This can result in some additional accelerations (both vertical (heave) and longitudinal (surge)) that will be experienced far more in the bow than the stern.
On the other end of the ship, the stern can experience a significant amount of propeller vibration that will not be experienced in the bow. Also, propeller vibrations aren't tied to wave action so they can be present even in calm seas.
Different people experience different sensitivity to these motions due to the differing frequencies ... propeller vibrations are a higher frequency than the response to waves. So, YMMV.
So, grossly over-simplifying this discussion:
Midship: experiences pitch, heave and roll
Foward: experiences the same pitch, heave and roll PLUS slamming
Aft: experiences the same pitch, heave and roll PLUS propeller vibration
Personally, I really dis-like propeller vibrations because they can actually rattle things like the ceiling panels in the staterooms. So, I prefer a mid-ship cabin (definitely the lowest of all motions) followed by a forward cabin. Aft cabins are my least favorite.