hmmm.... while aesthetically I'm drawn to the taller tank (24"), it seems that practical matters like lighting and maintenance favor the 20".
Next question: Are there any negatives to going wider (front to back), maybe, 30 inches?
Height and depth (width) are both a function of reach. I'm tall, have long arms and built my stand so that the top rim of my tank is at armpit height, so I can reach the sand in the front of my 30" tall tank. But anything towards the back requires forceps. An absolutely acceptable trade off to me, but perhaps not for every person. Unless you're using fluorescent, don't see why 30" tall is problematic. I have no issue maintaining high light animals on my sand bed with LEDS (or with MH before that). Ideal tank size to me would be 96" long, 30" tall and as wide as I could fit (36" or so in my current room). What's that, 450 gallons (too lazy to do the math)?