When comparing aria2 vs Rtorrent, the Slant community recommends aria2 for most people. In the question“What are the best Torrent clients?” aria2 is ranked 5th while Rtorrent is ranked 6th. The most important reason people chose aria2 is:
Due to aria2 being a CLI only tool it uses very little memory.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Small memory footprint
Due to aria2 being a CLI only tool it uses very little memory.
Pro Supports multiple download protocols
Has support for lots of download protocols including BitTorrent, Metalink, HTTP, HTTPS and FTP.
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).
Run 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.
Pro Free and open source
Pro Supports thousands of torrents easily
Pro CLI interface
Pro Reasonable feature set
rTorrent covers basics such as Prioritization, Selective Downloading, DHT, PEX and Magnet URIs. It includes MSE/PE for security. It has graphical and command line interfaces. Has UDP tracker and µTP data transfer protocol support. Even covers Super-seeding.
Pro No extraneous functions
Torrent is a CLEAN client. Meaning there’s no search engine, tools, or other things to bloat the program.
Pro RUTorrent is a great web interface for RTorrent
Cons
Con No native graphical user interface
While there is a web-based GUI, there is no native interface.
Con No HTTP/2 support
While the developer of aria2 is developing nghttp2 library, aria2 has no support for http2.
Con Ugly interface
Con Confusing to use
Con No IPv6 support
Con Requires manual router configuration
The client lacks support UPnP, NAT-PMP or NAT traversal for automatic router configuration.
Con Files can't be downloaded sequentially
Con No embedded tracker
An embedded tracker allows turning the client into a server offering an easy way of sharing files with others. rTorrent lacks embedded tracker support so another method of sharing or different client has to be used to share files.
Con No proxy server support
Con Lacks µTP transfer protocol support
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. rTorrent lacks this functionality.
Con No search
Built-in search engines allow finding torrents to download right from withing the torrent client. rTorrent lacks such functionality.
Con No web seeding
Web seeding support allows downloading file parts from an HTTP source alongside the swarm. It's usually used for long-term seeding and easing some of the load on web hosts that supply direct downloads by offering a BitTorrent download as an alternative while still ensuring that the file is always available in its entirety regardless of the swarm. rTorrent lacks this functionality.