What are some alternatives?
When comparing µTorrent and aria2, you can also consider the following products
qBittorrent - Lightweight and open source torrent client that runs on all major platforms.
JDownloader - JDownloader is a free downloading tool that enables you to download files from over a hundred hosting sites. The tool is compatible with Linux, Mac and Windows operating systems. Read more about JDownloader.
Transmission - Transmission has the features you expect in a BitTorrent client: encryption, a web-based interface...
Free Download Manager - It is a powerful modern download accelerator and organizer for Windows and Mac.
Deluge - Deluge is a full-featured BitTorrent client for Linux, Unix and Windows.
BitTorrent - BitTorrent is a peer-to-peer program developed by Bram Cohen and BitTorrent, Inc.