18" deep tanks

[Dearth]

Deep tank-
Pro-allows for fish swimming room allows for bigger fish and more growing room for corals, takes up a small area in room
Con- harder to reach the bottom, limited in your aquascape choices, limited places to put coral, harder to clean

Shallow tanks-
Pro-easier to light the tanks, lots of choices for aquascaping, easy to move things around and clean, can place a large amount of corals and move with ease
Con- limited in your fish choices, can limit coral growth, takes up quite a bit of space, can limit coral choices

The above listed are only partial lists and everybody will have their own ideas of pros and cons but the reality is that it's whatever you like

Personally I want both but limited by space and time and something I rarely get to see....money