Well, larger aquariums are easier to maintain than smaller systems. You usually run the risk of bacterial infection, ammonia poisoning, disease, fungus, premature death when you go with the smaller tank. It seems to be a common theme and it's easily avoided by investing literally a few more dollars into your set up.

Considering the cost of a 10 gallon tank at Wal Mart is roughly 13 dollars I see no reason to get anything less than that, again, just my opinion.