A9lh is currently the best exploit. It is launched milliseconds into boot, giving you a 100% bootrate, a fast startup time, and it negates the need for emuNAND. Because the exploit is installed on a low level, you can update your actual sysNAND and still use CFW. There's a guide here with information about A9lh and a tutorial on setting it up. Do note that it is much riskier to set up and much more complicated to set up than previous exploits. I'd recommend to only set it up if you feel very comfortable with modifying the 3DS and, while it doesn't seem to happen too often, are willing to risk potentially bricking your 3DS.
Was the NAND backup made with the Gateway launcher?
No, it was made with EmmuNAND9 :/