Strawberry if I had to have something visual with buttons.
cmus right now because it loads my rather large library in a split second. mpd works great as well.
More important than the player for me is sorting, though. Beets is my saviour. I could never sort the 5 or 6 albums I get by hand and tag them by hand.
I used to like deadbeef as well, quod libet is great. There really is something for everyone when it comes to something for music. If only there were as many great email clients.