Guys there is a thread here with the science on this. There have been a number of scientific studies comparing one type natural to another and artificial also.

As with all generalizations the answer depends on many more factors than just the question asked. I hesitate to answer with the results as they are specific to type and location and not good for a general answer. Do not take this the wrong way but take it as one factor to consider. We use both natural and man made so that should give you a hint that both are good. Also keep in mind that man made is often part natural. What if I take a bunch of big oak limbs and put them in a bucket with concrete. Is that man made or natural or both ?

The studies over all show a small but significant (> 5%) advantage to natural cover. But the man made still worked as intended and had an advantage of not deteriorating over time. Because the natural pond processes work on natural objects they had better growth and attraction results.

I will try to find the info.