Front to back distance is very useful when planting. Height is useful if you want to grow some of the plants that like to grow tall. Length just gives you the perception of a bigger tank. Those are just my opinions.
I know this thread is a little old, but just thought I'd add another consideration when choosing a tank size and that is how far you can reach into it. I know they make long tools, but long tools are much harder to work with than with your hands up close.
For my 72x24x24 tank I cannot reach the bottom back of the tank with my hands while standing in front of it as result I had to locate the tank in an area where I could walk all the way around it. If my tank were any wider I would not be able to reach the bottom middle of the tank without a snorkel.
I'm not sure that's so much the issue with the tank, rather the hood design layout you might have in mid or the stand height, some foklks are shorter and have shorter arms than others, by a factor of nearly 2X.
I design tanks for max access to the front lip, not hood lips in my way, easy open top designs and access is complete, I also tend to like chair height stands, so 24-30", I can stand a gets into most tanks.
For higher tanks or stands, I tend to shoot for about 40-45", but if the tank is tall, then it goes back to the 24" height, because if the tank is 30-48" high, it's means that view is 24" to 54-72" which is eye level or higher for most folks standing.