I'm not really a sponge fan as you have a big blob of black in your aquarium, and using plants to hide it eats dearly into your already small tank capacity. But having said I'm not a fan of sponge filters doesn't mean they aren't effective, they really are, and the link I'm sending you to is authored by a chap who has professionally maintained many tanks over time; he's a big fan of sponge filters.
I personally don't like the looks of them, that all. The link I am suggesting is a very long read. I too have a 10 gallon I will be starting in the not to distant future when I stop working for the Olympics (now the Paralympics) here in Vancouver (actually Whistler now).
There is an entire section on good cheap filters for small tanks and why he likes them. I'd print that section out and take it with you shopping. Fortunately there are some cheaper filters out there that work better than some of the more expensive ones - enjoy the read: