There is no single best answer with the information you’ve given. You need to look at the features to make sure they are suitable for you.
Some things to consider:
A larger solar panel will provide more charging power, giving you the speed you want. A larger solar panel will be more expensive.
Beware of solar chargers that use an internal rechargeable battery to store the power before recharging your iPod Touch. Those rechargeable batteries will eventually wear out, the same as the batteries in your iPod Touch.
Make sure that the solar charger is portable enough for you to take with you whenever you would need it. Smaller chargers are more portable, but they will also charge more slowly.

Solar Energy is one of the best sources of clean and green electricity. I think that we should build more efficient solar thermal power plants and solar cells. frequently. “