Recs.
Updated
Tixati is a resource light and minimalist torrent client that is highly configurable and extremely informative.
SpecsUpdate
Pros
Pro Full-featured
Tixati covers basics such as Prioritization, Selective Downloading, DHT, PEX, LPD and Magnet URIs as well as Broadcatching and Sequential downloading. 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 Tracker Exchange, IPv6, Super-seeding and proxy servers.
Pro Encourages optimizing settings and teaches how to do it
Tixati suggests ways to improve the overall download speed through pop-up tips, helpful hints and a tutorial available on the site. It explains how to properly throttle outgoing bandwidth to not affect download speeds, how to make sure all incoming connections are received and that DHT receives all incoming UDP packets.
Cons
Con Questionable interface aesthetic
Tixati has a 90s hacker-movies inspired high-contrast color interface that can be considered aggressive and unpleasant by some. Color scheme can be changed in the settings. Additionally, the amount of information Tixati presents that can be difficult to parse.
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. Tixati lacks this functionality.