As pointed out by those above - for DS roms you will need a seperate card as there currently are none available that can do both.
There has been speculation that there will be, but that'd mean waiting those options out. And considering the costs of a DS card, I see little added value there unless you don't need/want to get one soon.
In which case its a question of are you satisfied with just limited functions for a lower cost - in which case one of the R4 cards would do the trick.
Or would you prefer some additional functionality, but at a price - in which case the DSTWO would be your best bet.
In terms of 3DS cards your current options are:
- Trade in your 9.x device / sell it and get a 4.x one instead.
Then run with Gateway as the proven features are far superior to what else is available on the market right now.
- Get a SKY3DS which can run all games to date in a plug-and-play fashion and is currently being updated regularly with its template file and such.
At the cost of a 10-game-max-limit that may or may not be removed. So basicly consider it paying $8 per game.
It also lacks any additional features.
- Get a Gateway (or wait for the Gateway confirmation update and get one then).
The Gateway is looking like the "best" option for those that believe that the 10-game-limit from SKY is not acceptable.
However there is a strong possibility that the 9.x Gateway release will start off with limited functionality much like the 4.x Gateway originally did.
- Finally, and possibly even your "best bet" is to wait it out.
Wait out the storm and see who remains on the top of the pile.
More information will enable you to make a more informed decision, which means taking less risks on unproven cards/releases with unknown features or restrictions.
So ask yourself the following questions:
1 - Do I need this "now" or atleast very soon?
2 - What features do I value/desire?
Theoretically you could get a DS card now (either R4 or DSTWO depending on your preferences), then play those games while you wait for the 3DS storm to settle down.
Which I would personally consider to be a decent option especially if you never had the luxury of playing some of the many fine games that the DS has to offer.
You can only play one game at a time anyway and those 3DS games will be there still 3 months from now.