"Better", eh, what's that?
There is only what is more convenient for you at the moment. Just pointing out that you can use the Kobo itself as the SD card adapter, which is handy because you just plug in the Kobo and it connects, versus manually connecting to a folder every time. Always useful to have more options.
An SD card can be more useful for transferring books to someone else's ereader because you can load it up in advance. (Never seen much use in having one other than that, which is why I don't have one, but in this case perfectly reasonable.) So if you happen to have the Kobo by you, you can just go straight through that after a tiny bit of configuration, and if your mother is out with her Kobo, you can just load up the SD card with a manual connection.