The one and only card that actually works on the Nintendo 3DS with the latest 4.0.07 update. While other cards continue to struggle with making their cards compatible, the official R4 3DS team is the only card manufacturer that actually ensures that their cards work out of the box with every single update to date.

1. The Official R4 3DS Card From R43DS.org
The only card that works on the Newest Nintendo 3DS 4.0.07 Update
With every new release of system OS (or operating system) for the
Nintendo 3DS and Nintendo DSi and DSi XL consoles, there is a chance
of the R4 3DS cards not working, or rather, not being recognized by
the newly updated hand held system. As such, it is more important
today then it ever has been, to make sure that you purchase an
authentic card for your DS, DS Lite, DSi or Nintendo 3DS.
Far too often cone and copy card makers will simply stick an R4 3DS
label on their boxes and the cards, to try to sell you a card that while
may look authentic, is anything but. Unfortunately customers don't
realize this until an update has been released for their game systems,
and the said manufacturer of these cards has gone away and cannot
be found. What does this mean? You will end up having to spend the
exact same amount once again, for another card that you hope will
work.
At http://www.r43ds.org - the official r4 3DS store, you won't have to
worry about such things at all. Making sure that you get a card that is
an official card, means that you end up having the support of the
actual factory and manufacturer that stands behind their product, long
after you have paid for the item and received it.
The R4 3DS RTS version is one prime example of having a card that
continues to update the kernel and firmware all the while supporting
their previous and prior customers, without requiring you to go out
and buy another card. In fact, one of the only cards that works on the
newest Nintendo 3DS v4.0.07 update. While other cards stubble to
have their compatibility updated, the r4 ads rts is already fully
compatible, thanks to a kernel / firmware update that was release just
3 days after the 4.0.07 OS update was released.

2. The R4 3DS RTS official card from http://www.r43ds.org supports the
Nintendo 3DS 4.0.07 update, as well as the Nintendo DSi 1.44 update.
If you want to be certain that you are getting a card that will continue
to work despite updates to your game systems, the official r43ds.org
cards are the only cards that continue to work, and receive constant
kernel updates.
Visit www.r43ds.org to find out more, and to get the latest firmware
update for your R4 3DS Card.
If you already have the card, you must update your kernel firmware
right on your card itself. If however you do not yet have the card,
make sure to download the UPDATE file from the official R4 3DS store
in order to ensure that your new card will work on the latest Nintendo
3DS 4.0.07 updated 3DS consoles.