There is one subtle and telling difference between a solar power bank and a solar charger. A solar power bank has a battery, a solar charger does not. That one detail can determine which device you go for. If you know you will be going on a long trip and the weather may be temperamental, opt for a solar power bank. That way you can fully charge your device and even if the sun goes behind the clouds, you still have some charge reserved in the battery.
That ‘just in case’ aspect can make a crucial difference so you are not depending on the weather and sunlight exposure. Having power stored away is a comforting notion and saves you the worry of checking the weather. However, a solar charger is ideal for long backpacking trips when you know you will be out in the sun for hours. They are also comparably lighter and if you can rely on the sun they are more efficient and will provide a faster charge.