MY recommendation would be a modified iPod 5th or 7th gen Classic if you don't mind the larger size. These iPods can be upgraded with larger batteries and flash storage instead of a hard drive making them long lasting and robust.
You can do the modification yourself on iPod with a broken hard drive or buy one on eBay already modified. (Tip: The 5th gens are easier to modify than the 7th gens since they come apart a lot easier.)
Personally, I use a 5th gen Classic with 32GB of flash and a new battery. I modified it myself with a compact flash card and a new battery. It's been in use for about 3 years and I've had no real issues.
You can do the modification yourself on iPod with a broken hard drive or buy one on eBay already modified. (Tip: The 5th gens are easier to modify than the 7th gens since they come apart a lot easier.)
Personally, I use a 5th gen Classic with 32GB of flash and a new battery. I modified it myself with a compact flash card and a new battery. It's been in use for about 3 years and I've had no real issues.