Choosing a substrate sometimes depends on the individual animal.
Some iguanas defecate regularly like Swiss watches, and neatly in the same spots. Others go as they please anywhere they happen to be.
The #1 priority in a reptile enclosure is hygene/cleanliness. The cleaner and more hygenic, the less it smells, and the healthier the animal (and safer for you, health-wise).
Newspapers are cheap, easy to replace, but they are debated over the ink fumes. Not too eye-candy either. They are easily shuffled around, dragged, ripped, etc.
Barks do not absorb much, they can stink up the place, and cannot be cleaned, just replaced. Plus, some small chips could be ingested.
For those lucky enough to have turned a bathroom into an enclosure, tiles are a dream come true. Just wash, clean, drain, and you're done.
Others turn a garage into an enclosure, and first apply that garage-flooring coating that is water and chemical resistant. Again very easy: just wipe, wash and clean.
Fake-grass carpeting is another option, and kind of combines a little bit of everything. Nice to look at, absorbs well, and does not need constant replacement if done right. As I wrote many times before in the past, if applied as squares (say, 12"x12"
, each soiled 'square' can be quickly removed, and replaced by a clean extra one (always have clean extras on the side for replacement). Wash/clean/disinfect the soiled piece(s) and let dry. Continue the cycle. Once a day the whole floor can be sprayed-on with a pet-safe deodorant to keep any odors down (due to the humidity and heat in the room).
Depending on how often your iguana poops, it is a twice/three-times a day ordeal, not too bad. It is obviously not as cheap as paper or bark, but in the long run I think it's worth it.
Do some research and reading for other options. I hope this helped!
-IJ