I've tried all types of MP3 players... what did I get? An ipod mini.
Realistically, I'm not gonna use more than 4GB. I only keep good music on my ipod, and I'm only using 2.5GB. That adresses the size issue.
Ipod minis are quite compact. You can clip them to things, use bands on your arms, etc. They can go almost anywhere. Portability sorted.
The navigation. It's REALLY easy - even my dad could use one, and thats really saying something. They just feel so right and easy to use.
The battery life is also great. I've pumped 16 hours out of mine, just about, on a regular basis - of constant playing - despite it only having an official 12 hour battery life.
If I lost my ipod, I'd probably die. End of.