I've used the Quod Libet music player since 2005. Mostly happily, despite the occasional really weird bug. The core of Quod Libet for me, the thing that no other player has, is the album list, just a big list of all available albums, with cover icons, and an easy way to limit the display to ones matching a search term. (I'm not one of those people who does complex, detailed playlists; I tend to play one album at a time, in order.) Quod Libet has lots of other nice features, including a great metadata editor, but the album list is the only thing I use daily.
I mostly run Quod Libet on relatively slow machines (with decent speakers), with the display fed to my laptop. Lately it's been feeling a bit slow to scroll around in the album list with hundreds of albums and album icons being displayed over the network and everything running on an old laptop, or an overloaded server. I've known about mpd for a long while, and it's clearly a better fit for how I use servers to play music, but I could never stand to use any of the clients for long.
Today I hit the triple cocktail of evil bugs in Quod Libet described in Debian bug #413284. This is a potential last straw type bug, that's been open since March, and which I'd read before and hoped I'd be lucky enough to escape.
This motivated me to try the Sonata mpd client again. It has a very clean looking and generally good interface, though like all mpd clients, it annoys me by being based around a playlist, and not making it easy to just select an album from the library and immediately start playing it.
But there's a trick that makes it usable for me. I added all my music to the "playlist" (using the mpd command line) and ignore the hard to use library. Since Sontata does have an excellent type-to-limit-display feature, I can just type the name of an artist, album, or track, press enter, and it jumps to it and starts playing.