Originally Posted by Dave H

In general if a higher voltage is available that is preferable, generally more efficient and cooler operating. And depending on the charger and packs may allow for more power - higher amp charge rates.

One consideration, while not always necessary it's best to avoid a supply voltage in the same range as the battery pack. For example a 12V supply charging a 3S lipo causes the charger to switch between buck and boost modes as it charges. Some chargers, even some otherwise well regarded ones, are less than perfectly stable while making the transition. Generally it's not a huge issue, but not ideal, avoiding it if possible is reasonable.

Give us some more details on your equipment and packs and we can be more specific about your situation.