iTunes is probably my favorite to use. The ease of finding what I want to hear is hard to beat. The problem with iTunes is that it only supports the formats Apple wants it to support. mp3 is there only because its the blind favorite of the masses. If it was flexible and supported other files I'd probably actually use it despite the bloat.
WMP, worse than iTunes, you can tell because they tried to change it to be more like iTunes when they moved from 9 to 10...if you're copying someone it can't be better.
Winamp can do the same, but with too many windows, winamp feels almost as if it has been built for people with small music collections. And now for some reason my winamp seems to refuse to correctly read and then display the information from the tags on my FLAC files. A rediculous and unexcusable downside as it is now harder to search for what I want to listen to. I'm about to give up on it as it doesn't seem caught up with the times. Winamp hasn't really undergone any drastic changes, especially with 5 being a sort of hybrid of 3 and 2...if it doesn't die I'd hope we see a drastic change in design with a next version.
foobar, a great idea, problem is that it was made by nerds. Just like with Linux it isn't noob friendly, the interface is NOT user friendly, you pretty much have to be an expert computer user to like it. The interface is crap unless you know how to mess with it, and your average noob computer user is not going to give it enough time to figure out it isn't a complete crap program in their eyes. A program like this will never be the best. Despite such a fact, it could possibly be the best solution, simply because of how imperfect all the other players are. Thats pretty sad if you ask me.
What would be the perfect player? A single window player with a sharp but clean interface (not as dull or as difficult as foobar, and no more flashy than iTunes, Winamp's media library woud be acceptbale if you could just play music straight from it without the other crap windows) with unbiased format support. Tabbed organization is nice, something foobar does well. I like being able to keep my different formats separate. I dunno I guess basically a player that you can customize to work and look the way you want it to. Right now foobar does that the best. It sure isn't pretty to look at, but then that's not what we have these programs for is it?