I like tangs that like to swim, which makes length the most important for me. Also allows you to have multiple rock islands that are not connected, but still looks good. I feel with width you would notice it significantly more than a guest seeing your tank for the first time. The depth is important, but definitely lesser for my taste. Height is a double edged sword. A tall tank looks impressive but adds nothing to swimming and aquascape room. Also trying to clean tall tanks is a pain in the butt. From an owner standpoint I like shorter tanks, from a spectator standpoint a tall tank can be impressive.