When comparing aria2 vs put.io, the Slant community recommends aria2 for most people. In the question“What are the best Torrent clients?” aria2 is ranked 4th while put.io is ranked 17th.
Ranked in these QuestionsQuestion Ranking
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.
Pro Can automatically start downloading content once it's available
Broadcatching is a method of automatically downloading content as soon as it's available. Broadcatching in BitTorrent clients is usually implemented via RSS.
Pro Popular torrents are instantly available
Due to server side caching popular torrents can be downloaded quickly.
Don't need to have a machine running to download.
Con No native graphical user interface
While there is a web-based GUI, there is no native interface.
Con Unknown underlying technology
It is unclear what BitTorrent protocol features or extensions are supported by the service.
Con Not free
Plans start at $9.99/mo.