The general rule of thumb for tanks or tubs in inches is the length + width = the max length of the snake.
So the 106 Quart one is 33in.+19in.=52in. which is about the max size of what you should have in their
And the other one is 44in.+19in.+63in. max snake
And the 44 inch one is shorter which means it is easier to heat.