If I wanted more corals than fish...smaller more cube-like dimensions. If I wanted lots of nice fish, tangs included, I would do a larger tank, 6+ feet in length. 
 
My ideal or dream tank would be in the center of a room with bar seating all around it. 6'X4'X2' ... some day! 
 
But like steve said....realistically its more based on where you are putting it, and how much space is available. 
		
	
		
		
		
		
			
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