Is it better to let my battery die before I charge it, or when it is low?

Should I let the battery go down to 0% before I charge.

No. Doing that on a frequent basis will shorten the life of your battery, and whoever told you otherwise was wrong (such a policy only applies to nickel-based batteries, and even then it's debatable whether that's a useful practice).

You should charge the iPod as often as possible/convenient. Only let it run down to the point where it shuts off once every month or so; this helps keep the battery life indicator and charging circuitry calibrated but should not be done too often.

Regards.

There are too many people telling "truths" that are just not true, but based on something else that is true or something that used to be true. I see this in all aspects of electronics as well as other fields.

Never let a LiIon battery die.
Never let a lead acid battery die.
At least occasionally let a NiMH or a NiCd battery die but be certain you do not allow one or more cells to get charged in reverse which is very possible if you let the voltage drop much below 0.9v per cell.

Many PDAs and cell phones used to use NiMH or NiCd batteries. Few if any do now days. Almost all laptops and PDAs and cell phones use lithium based batteries now days. This will likely change in the future.

I point out these four battery types just to show you how things get twisted. It is far better to get your information from multiple sources on issues of this matter and consider where your source gets its information. Don't just blindly believe or you will likely be costing yourself undue expense as well as using up earths resources needlessly. But, waste is good for the economy so all is not lost (just joking) 😉