I'm going to be moving next year and am planning to upgrade from my 30 gallon tank. People on this forum convinced me that I ought to get a bigger tank than I originally thought. At this point it's between a 120 and 180. Besides the obvious, what's the difference between the two sizes, ie is one dimensionally more balanced than the other? If they're similar in terms of dimensions, then I might go with the 120, because I don't want to deal with more water changes/live rock that a 180 would demand, and there really aren't any fishes I'm interested in that need bigger than a 120 gallon (except maybe a yellow tang, but I'm not sure it couldn't live in a 120).