The only ones I can give advice on are the Creative Zen mini, Zen Sleek and iPod Video 30G. I had the Zen mini first and it lasted about six months (keep in mind I was in Iraq). I only took it out on a couple of missions, though, and always kept it in my pocket or covered someway. However, when it died, it really died. There was no reloading the firmware, no reformatting the harddrive, nothing.
So, I upgraded to the Zen Sleek (20G). I loved it (at first). But one day, I took it to the pool with me (still in Iraq ... yeah, we had a pool) and it froze up. Okay, fine. I thought. I'll let it cool down and it will be fine. It still won't do anything. I can turn it on but it never gets off of the load screen. And once you turn it on, you have to let the battery run out because it won't go off. I went through their troubleshooting guide on Creative's website and it seems several other people were having the same problems. So I have to send it back. Which is a shame on both because I really liked the extras in the Creative Zen line ... they included an FM radio (I could pick up Kurdish and Iraqi stations

) and a built-in voice recorder (that saved my butt more than once when I had to cover ceremonies over there ... I just turned on the recorder, put it on the podium, and got EVERYTHING I needed for my story)
This is when I broke down and bought an iPod. To tell you the truth, I did not want to buy one at first because it was the "trendy" thing to have. If something gets over commercialized I tend to shy away from it. Anyway, I love the friggin thing

I take it to the gym (the 20G Zen Sleek is to bulky/sensitive to strap on your arm and go running ... maybe not a selling point for many, but I have to have my music when I run), play it in my car, plug it in to my home theater system at home ... I even keep pictures from Iraq, photos of my neices and nephews, my bf ... all of it on there.
Okay ... a quick rundown on what I know
Zen mini 5G
+
Voice recorder (10 hours)
FM Radio
Compatible with Windows OS
Don't know about MAC
Plays regular MP3 format
Comes in multiple colors
Can be worn while running/working out
-
Seemed to burn out quickly
Locked up often
On/Off button stopped working
If dropped, the battery pops off
Zen Sleek 20G
+
Voice recorder (10 hours)
FM Radio
Compatible with Windows OS
Don't know about MAC
Plays regular MP3 format
Color screen
-
Burned out really fast
If it overheats, it will probably go out
Bulky
Not recommended for gym or sports use (that is from Creative)
Creative tech support is not very customer friendly
iPod Video 30G
+
Sleek design
Big color screen
Compatible with Windows OS
(and of course MAC)
Comes in two colors
Can be worn while running/working out
Includes games
Holds photos
Plays videos ... including movies and TV shows
A lot of accessories are available for this thing
It's shiny

-
You have to convert all of your music to the iTunes format
Only plays Quicktime videos
Pretty much all accessories have to be purchased separately ...
this includes the charger

You don't get the software in the kit you buy ... but it's a free download
Sorry for the really long post ... hope this helps some.