Pros and cons to anything. I know many use Aspen, some use Cypress. Many use simple paper products such as newsprint, papertowels, or the red rosin paper from Home Depot. Currently, I am using good old paper towels for all my larger enclosures.
And I am sure you'll have messes to clean in those back corners. I have a couple thin putty knives that work well and are easy on the cages.