Originally posted by: Aflac
The X5L supports more formats out of the box, and has better sound quality (though the difference is nearly negligible, since both are very good), and is a more "open" player. The Vision:M is made by Creative, so you KNOW they're going to add proprietary crap onto it (transfer software, for the most part). Also, the Vision:M has no Rockbox support, while the X5L does. On the other hand, the Vision:M has a much better GUI and physical interface in general, as it's much easier to work with a touchstrip than it is to work with a stubby joystick. Also, an obvious point is that the Vision:M has a much better looking screen and is more popular (meaning more 3rd party support).
All considered, if you're looking to get the best mp3 player for music, I'd have to say it's the X5(L). However, I have absolutely no idea how well either of these microphones work, so I may have written that all up for nothing

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The Vision:M supports MP3, WMA, and WAV, while the X5 supports lots more, most significantly, as PurdueRy stated, Ogg (does it support FLAC?).
As a possible-testimony to the Creative Vision:M's microphone, I have a Zen Sleek and it records well - good quality and reproduction. However, from my experiences, it does not pick up people talking at normal volume levels 15 feet away. I don't think any built-in microphone will do that, though...
As an alternative, you could buy an mp3 player, then get some sort of voice recorder that will do the trick for you.