Over the years I've consistently said the iPod Classic is the device to buy for the serious music lover who wants as much music as possible at their fingertips.
Capacity is the most obvious reason, particularly if you have a large music collection and/or music ripped at a high quality level, such as Apple Lossless, then the lower capacity devices just don't enough storage space. However I've also felt, from entirely subjective listening experience, the Classic just sounds better than the Touch or even the iPhone.
Well I can believe my ears, there are differences between the Classic and other devices. The Classic has a better digital-to-analogue converter (DAC) and more effective amplifier for the earbuds. Even though the underlying music files may be the same using these two components will deliver a far better listening experience. So, if you're thinking about investing in a new iPod you might want to snap up an iPod Classic PDQ, they might just be replaced later this year by another device.