I use the reptizorb liners for 41qt vision tubs, which I get here.http://superiorshippingsupplies.com/...5/shopbrowse/1
I'm fairly pleased with them, they soak up any liquid spills so the animal isn't sitting in moisture (much better than even the viva paper towels) and since they're all one piece it's easy to remove the liner to clean (I kind of fold it around the poo like an envelope, then shove everying in a plastic baggie). I would say their smell absorbing capability is pretty similar to aspen.
The best part is that because they're cut to fit specific tubs you can just store them all in an empty tub and pull fresh ones out as needed. Much tidier than aspen or coco coir since I inevitably get those all over the floor.