In an attempt to determine which of the two get the best download speeds, University of California researcher Marios Iliofotou together with colleagues from Telefonica Research inspected the download speeds of more than 10 million BitTorrent downloaders last August. The results have been collated in a short paper (pdf) and it turns out that there are some big differences between the two BitTorrent clients.

As an initial sample the 600 most popular torrents on the Pirate Bay were used. The torrents were tracked for a month and a representative sample of one week was used for the final analysis. For each torrent an equal number or uTorrent and Vuze users were selected and these were also matched by ISP, so the type of torrent or ISP could not influence the results.

The research revealed a remarkable speed difference with uTorrent users getting 16% higher download speeds than Vuze users. On average uTorrent users reached a 176 Kbps download speed while Vuze users were stuck at 151 Kbps on the same torrents and with the same ISPs.

More detailed analysis revealed that uTorrent users get faster downloads on all of the 30 most used ISPs, except Verizon where there was virtually no difference. On 10% of these ISPs, uTorrent users were downloading 30% faster than Vuze users.

To find out what might be responsible for these speed differences the researchers reverse engineered both BitTorrent clients. They speculate that the distribution of upload capacity to peers is one of the underlying reasons. On average, uTorrent shares data with more peers than Vuze.

Differences in how the clients handles connections to ‘neighbors’, how they discover new peers and when they decide to close connections are also mentioned as factors that may have led to the observed speed differences.

The scope of the report is limited to Vuze and uTorrent but in future work the researchers hope to include other clients too. In addition they plan to confirm these results in a lab environment, to try and find out what constitutes the fastest BitTorrent client.

“This work does not aim to design the best BitTorrent client, but to bring to the attention of BitTorrent implementors and users that some design choices have a significant effect in practice. Even though in our study uTorrent appears to achieve faster speeds than Vuze, we do not claim that uTorrent is the way to go,” the researchers write.

“We hope that our preliminary findings will open the door for new research efforts to better understand the impact of design choices in the performance of real-world BitTorrent implementations. Ultimately, we see such research efforts leading to the design of better P2P systems,” the researchers conclude.

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Many BitTorrent users are looking for the holy grail that will boost their download speeds to the maximum, and tweaking your client can indeed help a bit. However, selecting the right torrents is far more important, and those are not necessarily the torrents with the most peers. Bram Cohen, the inventor of the BitTorrent protocol addresses this common misconception in a recent blog post.

“Cohen designed BitTorrent to be able to download files from many different sources [...] the more popular a file is, the faster a user will be able to download it, since many people will be downloading it at the same time, and these people will also be uploading the data to other users,” writes Cohen while quoting an erroneous article.

This is indeed an explanation we often hear – the more people who download a file the better – but unfortunately it’s not very accurate. Or to put it in Cohen’s words, this description of BitTorrent is “somewhere between grossly misleading and wrong.”

Cohen goes on to explain why: “There’s a classic fallacy because if one person stands up during a concert they get a better view, then if everybody stood up during a concert they’d all get a better view. This is of course is not true – they wind up slightly worse off by all standing, because they all compete with each other for a view.”

So how do you get the most out of BitTorrent then? Or to put it differently, what torrents perform the best and generally give you the fastest download times? We’ll try to explain it as simply as possible leaving math out as much as possible.

The fastest torrents will be those where downloaders (leechers) can tap into the most upload capacity. If you have a swarm (seeders and leechers) with a hundred people in total it will be faster when there are relatively more seeders. Why? Very simply it’s because seeders don’t download while their upload capacity is available for the leechers.

Many people understand these basics. A torrent with 30 seeders and 70 leechers (30% seeders) will go faster than one with 10 seeders and 90 leechers (10% seeders). However, it get confusing when you compare swarms of different sizes.

For example, a torrent with 30 seeders and 70 leechers (30% seeders) will generally be faster than one with 500 seeders and 2500 leechers (20% seeders). Why? Simply because the swarm has a smaller percentage of seeders. When picking the right torrents to download, the percentage of seeders that a swarm consists of is the most important thing to look at.

A higher percentage of seeders means that the average upload capacity available to the leechers will be higher. The fact that leechers also upload themselves is irrelevant because all peers have more download capacity than upload capacity. The seeders make the difference.

This is one of the reasons why private trackers generally have such great download speeds. Since users are required to seed as much as possible, they have torrents with 100 seeders and only two or three leechers.

So what can we learn from this? If you’re looking for fast torrents pick those with the best seeder/leecher ratio or the highest percentage of seeders. Or when you don’t have a choice, don’t complain about slow speeds when there are only a few seeders in a large swarm. Perhaps even more importantly, remember to seed as much as possible if you don’t need your upload speed for something else.

Source: TorrentFreak, for the latest info on copyright, file-sharing and anonymous VPN services.