Mini disc is a real hassel. First is that immensly tiny screen... but if you're going to be active, I suppose that doesn't really matter.
Sony likes to keep track of priacy, so you could have some problems if you don't transfer music the right way... it keeps what songs are loaded outside, and what songs are in. I've heard that it won't let you copy stuff back on your computer if it isn't already there first. I'm not so sure about this... if someone would like to correct me, please do.
Rumor there was a third party program that let you transfer stuff unmonitored, but that's just what I heard from a friend at school.
The interchangable discs are a definite plus. Much much smaller than CD, extremely hard to cause a skip, and... relatively cheap. And their easily rewritable, so they're totally resuable. The hiMD units are nice, but as I said before, without the use of a large screen, navigation through a gig of music can be a hassel.
It just depends on you as a person... if you like to have lots of music, you can go with MD. You can lable certain discs to contain certain types of music and the like.
But with flash, you're stuck with the songs you already loaded. Then again, you may have some sort of style of music that you listen to when outside, so you already know what kind of music to load on your flash player...
Flash is the best for durability, but even if your MD player skips, it's not going to kill it like a harddrive. As far as I know, skips on an MD player are harmless, just like on that of a CD player.
It's all up to you, and I'd go with either...
Rio makes some pretty nice flash players. Many of them have expandable flash memory for up to 1 gig SD cards. Just note, they will really drain the battery if you have an EQ activated.
iRiver also makes some decent ones. To note, many iRiver flash players also have a line in, so you can record music, or voice. But they are flash, so they are limited in how much they can contain. No removable memory.
You'll need someone else to recommend an MD player, I have no real extensive hands on dealings with these, except for one of them.
