In the scheme of things the price I find the price difference between the two inconsequential.
Sysnand is the factory firmware, emunand is a copy that runs off the mSD card and allows you to update it to later versions for features and compatibility while maintaining sysnand for the exploit. While technically emunand is not required there is little reason not to use it. Currently it can be up to 9.5 on the n3DS. A feature of gateway, firmware spoofing, allows games to run on lower firmwares. 9.6 introduced new encryption that has not been broken yet, but is not a problem currently for games and will likely not be for some time. This is a small concern but a real one for the future. Gateway has always come through in the past and that is the most anyone can say about it. Neither card is risk free or absolutely future proof. So far the mouse has always won, but the cat may sooner or later.
You can easily upgrade emunand to 9.4 with a rom or 9.5 with a few online methods. All current games will run even on Emunand 9.0 currently with the spoofing, although higher is needed for amiibo support. "Classic mode" allows you to run retail carts without updating sysnand.
Gateway is the far better choice if you have an exploitable firmware like you do. The chips on Sky are not updatable so if Ninty blocks it, game over for future fw updates. Yes you can always revert to the original state.
Currently there is a recycled exploit that goes by many names such as Mset and DS profile that allows you to enter the exploit without any carts other than the gateway once set up. Although playing DS mode games as an kick you out and require cubic ninja or Oot to get you back in. You travel so a small case with a few card slots would come in handy so you are never caught with your pants down. They cost about $10
Thank you very much for your quick and detailled answer! I appreciate that.
So, if I want to play games offline, it shouldn't matter if I'm on emuNAND 9.5, right?
What if I want to play online?
I own a game that wants to update to 9.5, can I use that to update my emuNAND?