The biggest problem with tubs is their inconsistency. It seems like Sterlite and Rubbermade both will change their tubs every couple of years. I can't tell you which is better. Both brands have their pros and cons. Iris tubs are nice but about twice the cost of Rubbermade and Sterlite and can be hard to find certain sizes.

As far as size, adults colubrids will do fine in 27-41qt. tubs. Sub-adults can be kept in the 12-15 qt. tubs. Sterlite and rubbermade both recently add a new low profile container with ample floor space that would be perfect for sub-adults. You can find these at Wal-mart in the container section and Target in the sewing/laundry section. I recommend just choosing the one that you think best fits your situation. There is no perfect tub.