Here and elsewhere, a lot of people try to correlate the location of their room with seasickness. If, in theory, you will feel less movement mid-ship/lower, the variation between different spots will not be that great and will vary based on the size, frequency and direction of the waves. Add to the mix the fact that specific movement (up/down, left/right, slow, fast) will affect everyone differently and that you spend your time all over the ship and not just camped in your stateroom.
My advice is to chose your stateroom based on other considerations, like noise from the hallway or the deck above, closeness to Cabanas or the stairs, etc. If you hit a patch of rough seas, you'll feel it anyway.