Reviews and Ratings
As it says by itself, SMPlayer is a great MPlayer frontend.
It provides me a pretty, easy-to-use interface to control MPlayer. SMPlayer supports a well-balanced number of MPlayer filters, and has many configuration options, although the interface is never cluttered.
SMPlayer also has some great features to download and configure subtitles. So basically, it combines the power of MPlayer with a great GUI.
SMPlayer also offers many (up-to-date) translations, so you can almost always use it in your own language.
SMPlayer has a fast development cycle, and the devs are always willing to listen to your problems and feature requests.
One disadvantage is that some of the newer features of SMPlayer require you to have a very recent (SVN) version of MPlayer, and most Linux distro’s only provide “stable” versions.