There's a third way ... Make an array of all the skins and just use something like:
return SkinNames[ skinid ]
Uses more memory since it needs to load the whole array in order to return one index. The switch method is better in this case.
If you only need to use this function minimally, then yes, you would be correct. However, if you have to use this function often, then no.
I'm pretty sure the array is the better choice. Just keep it on the root table and access it when needed. Accessing a specific index of an array is much lighter on memory. With the switch method, you are pretty much doing the same thing as a loop. A switch statement runs through all the options until it finds what it needs. Not only is the switch statement slower, it consumes processing that could be used elsewhere.
I'm not sure if this next part is correct, but I'm pretty sure there is one core linear process, in which the current processing needs to finish before the next is started. Unless you are using threads, I think that this would be held up by a switch statement needing to do its thing.