I would say that it depends on your first filter and your stocking levels. Why do you need/want a second filter on a 29?
Personally, I love sponge filters, I keep one in all my tanks, even my display tank. There is a lot of space in your tank if you focus away from the bottom. I have a 6x6 Mattenfilter
cube attached to a powerhead at the top of my 75 & 55. It is easy to take out and clean weekly, and I am amazed at how much gunk I rinse out. It also allows me to be a bit lazier in cleaning the canister.