Gateway works with emunand and doesn't allow newest firmware, far more complicated than just using a Sky3DS. I would have to downgrade my 3DS in order to use it, I have one since long time. Plus it comes with two separate cards, one for flashing and one for the games. As far as I know, every time a new FW comes out, you have to reflash, too much hassle, Sky3DS just works out of the box. Just go to the Gateway homepage to look for yourself.

The cheat ability was only added recently, and so far I think there's only 5 games working with cheats.

Never heard of the SCDS2+, I have the SuperCard DSTWO for the DSi, and I have to say that it works quite well.