When comparing BitTorrent vs aria2, the Slant community recommends aria2 for most people. In the question“What are the best Torrent clients?” aria2 is ranked 4th while BitTorrent is ranked 18th.
Ranked in these QuestionsQuestion Ranking
Pro Clean and easy to navigate user interface
A clean, visually-appealing interface that’s incredibly simple to navigate and cuts down on clutter by allowing unwanted elements to be hidden.
Pro Additional features with the purchase of BitTorrent Pro
If you pay $19.99, you will get features such as removal of advertisements and added support for an internal HD media player.
BitTorrent covers basics such as Prioritization, Selective Downloading, DHT, PEX, LPD and Magnet URIs as well as Broadcatching, Sequential downloading and Search. It includes MSE/PE for security. It has graphical and web interfaces. Has UPnP, NAT-PMP, NAT traversal for automatic router configuration. Has UDP tracker and µTP data transfer protocol support. Even covers IPv6, web seeding, Embedded tracker, Super-seeding and proxy servers. And it auto-updates.
Pro Free and open source
Pro Supports multiple download protocols
Has support for lots of download protocols including BitTorrent, Metalink, HTTP, HTTPS and FTP.
Pro Small memory footprint
Due to aria2 being a CLI only tool it uses very little memory.
Pro Remote control over simple standartized RPC
XML or JSON-based RPCs can be used to control aria2 remotely with both APIs completely documented. Simplest client that uploads torrent to be downloaded is 3 Python lines long (no 3rd-party libraries, only stdlib).
aria2c --help=#rpc to see more.
Pro Third parties offer a clean web interface
Some web interfaces consist of pure HTML+JS, no server-side needed (except aria2c of course). It uses the same RPC that can work even over WebSockets.
Con No tracker exchange
Tracker exchange functionality allows peers to exchange information about trackers of a given file. It is another way of ensuring that the file is downloaded from the optimal source. BitTorrent lacks this functionality.
No source code is publicly available. As such there's no way to independently check what security and privacy features are implemented and how as well as whether there's any malicious code or not.
Con No native graphical user interface
While there is a web-based GUI, there is no native interface.