For me, it's easy. iPod 5th generation enhanced. It has a great bright display, good battery life, 80GB space out of the box, easy to upgrade to a larger HDD or CF card/SSD. And it has (to me) the
BEST click-wheel of them all. Very responsive. A runner up is my 2009 iPod classic (the last of 'em). But the click-wheel just doesn't work as well for me. Even if the interface is a little prettier.
[url=http://i.imgur.com/pMYWEfcl.jpg]Image[/url]
I've got her filled to the brim on the stock 80GB drive, roughly 7,000 songs (many ALAC). It gets charged/synced once a week and then rides in my truck for the rest of it.
Battery lasts just like new. Say it goes through one battery cycle per week since it's been around (2006). There's 52 weeks in a year and it's 2015. That's about 468 cycles so far. I kind of wonder how many they're good for. Considering it's out in the heat in the summer and well below freezing in the winter. Keeps on ticking.
My iPod classic might go through one per month if it's lucky. It kind of sits around. It's intended to be a replacement for this when/if it dies. But also nice to have since they got discontinued. I got it middle of last year, still pristine with case, box, and unopened accessories.