This was concluded in a recently published article in the online journal ‘firstmonday’ compared the sharing behavior on 6 BitTorrent sites.
The article compares bt.etree.org, piratebay.org, torrentportal.com, easytree.org, btefnet.net and alluvion.org. The data appears to be a little outdated, because both easytree.org and the famous bt.etree.org were shutdown in spring 2005.
One of the main conclusions of the researchers is that a relatively small percentage of peers is responsible for most of the uploading. The top 10% sharers upload just as much as the rest of the people in the swarm.
Another interesting finding is that the highest percentage of seeders can be found at The Piratebay (29%), and the most sharers at easytree (59%). This can be explained by the fact that easytree is a private tracker, enforcing “healthy” share ratios.
Unfortunately, the authors make a big mistake when they suggest that RSS feeds might be responsible for the higher seed percentages at btefnet.net. At the time the data was collected (early 2005) only Azureus had experimental RSS support, and only a few people were actually using it.
Personally I think it it hard to make comparisons between there six torrent sites. It is nothing more than comparing apples and oranges, they offer different content, and target a different audience.