Either device would be a great addition to your wireless network, but the performance of each would be different according to how they are installed. The EAP600 works best when ceiling mounted, so it would be the device to get if you want to install the WAP on the ceiling of the second floor. The ECB600 is best used when on a desk or mounted on the wall with the antennas upright.
Figure 1: EAP600
Figure 2: ECB600