When comparing aria2 vs Deluge, the Slant community recommends Deluge for most people. In the question“What are the best Torrent clients?” Deluge is ranked 3rd while aria2 is ranked 5th. The most important reason people chose Deluge is:
Deluge is free, ad-less and open source software licensed under GPL with source code available [here](http://dev.deluge-torrent.org/wiki/GitRepo). Being open source allows anyone to check if the software has no malicious code, is secure and respects privacy.
Ranked in these QuestionsQuestion Ranking
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).
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 Free, ad-less and open source
Deluge is free, ad-less and open source software licensed under GPL with source code available here. Being open source allows anyone to check if the software has no malicious code, is secure and respects privacy.
Pro Can encrypt traffic
MSE/PE or Message Stream Encryption/Protocol Encryption is BitTorrent traffic encryption method designed to improve privacy. It also attempts to make it harder to identify BitTorrent traffic by third parties such as ISPs that can choose to throttle it.
Pro Good web UI
Deluge has a web interfaces that can be used to remotely control torrents.
Deluge covers basics such as Prioritization, Selective Downloading, DHT, PEX, LPD and Magnet URIs. It includes MSE/PE for security. It has graphical, web and command line interfaces. Has UPnP, NAT-PMP, NAT traversal for automatic router configuration. Has UDP tracker data transfer protocol support. Even covers IPv6 and proxy servers.
Deluge weighs under 15MB.
Pro Functionality can be extended with a variety of plugins
As is, Deluge is very stripped down, but its functionality can be increased via plugins. As such Deluge can have only the functionality that is needed and skip any other reducing resource usage.
Pro Has a command line interface and a daemon
Deluge can be run in text-only mode via the
deluge-console command. Requires first running the deluge daemon
deluged. Utilizing the deluge daemon
deluged allows remotely connecting to it, and using any front-end interface.
µTorrent can be run without having to be installed. It can be put on an external storage device (such as a USB drive) and run directly from it. A portable version of Deluge can be downloaded from SourceForge.
Pro Neat and clean look
The GTK elements aren't the best looking in the world, but they are very tidy, minimal and easy on the eyes.
Pro Utorrent compatible
You can download using both clients µTorrent and Deluge on any supported operating system.
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 Files can't be downloaded sequentially by default
Sequential downloading can be used to stream media files such as video and audio while the download is still in progress. By default, Deluge requires waiting until the complete file is downloaded before it's ready for use.
But it should be mentioned that there exists a plugin: https://github.com/JohnDoee/deluge-streaming for video streaming from Deluge.
Con Demon not lightweight as expected
While it has been improved a lot in the last years, when it's used in "headless" mode, the python demon still tends to use more resources than expected. It's noticeable especially on devices like the raspberry, and for instance, rtorrent and transmission use much less CPU.
Con Includes minor UI issues
Deluge has minor UI issues such as presenting "delete with data" as the most prominent button when removing a torrent from a list of downloads, or the way it resets its size when maximized from tray forcing a resize each time.
Con Does not preload magnet data
If a magnet URI is used there's no way to get information about contents or perform any kind of actions (such as selecting what to download) before the download has started.
Con No web seeding suport
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. Deluge lacks this functionality.
Con No super-seeding support out of the box
Super-seeding is an algorithm used to allow downloaders become uploaders quicker. Deluge lacks support for this functionality out of the box. However, the ltconfig plugin can enable this setting: http://forum.deluge-torrent.org/viewtopic.php?f=9&t=42887.
Con Keeps Unwanted Files (Poor selective Download)
Deluge creates all the files even those that you marked "not download". Making your directories messy.
This is very bad when you want to create a drive specific for large files and you are unable to delete or move small and unwanted files, such as a video partition with large allocation unit.
[qbittorrent doesn't do that]
Con Doesn't shows all time uploaded and downloaded data
Con Hasn't been updated in a while
As of writing of this, there has not been a new release in ~1.5 years.
Con Can't "force start" downloads
There's no way to manually override settings for download queuing that's available in other torrent clients. For example, if there are 2 files in the download list and the software is configured to queue just one at a time there's no way to force a download of both without changing the settings. A workaround plugin can be found here.
Con CPU usage does not scale well with number of torrents
Deluge uses ~10% of one Core i7-2600 core with ~1700 torrents loaded, even if all the torrents are idle.
Con Lacks µTP transfer protocol support
Con No built-in search engine
Built-in search engines allow finding torrents to download right from withing the torrent client. Deluge lacks such functionality.
Con Naive search function
Searching for torrents or files within torrents is difficult because it relies on the user to input the exact title with the right index for each character.
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. Deluge lacks this functionality.
Con No embedded tracker
An embedded tracker allows turning the client into a server offering an easy way of sharing files with others. Deluge lacks embedded tracker support so another method of sharing or different client has to be used to share files.
Con Doesn't seed
Con No built-in broadcatching support
Broadcatching is a method of automatically downloading content as soon as it's available. Broadcatching in BitTorrent clients is usually implemented via RSS. Deluge requires manually selecting each download by default. Fortunately, there are multiple plugins available that add this functionality with the possible caveat of plugins not having the same quality standard as the client itself.