atmosphere is the base of all CFW, but is incomplete right now, is said that it will be release on the next weeks but we dont know when
Every "cfw" (or starter pack) is based on atmosphere/hekate/tinfoil. They're literally all the same codebase, just some are packaged with anime boot screens.
SX is good if you support blatant piracy, don't care about GPL and just want to play some pirated games. (Cus you know that's all it's good for.)
Please keep in mind there is also RajNX. The lead developer publishes and attributes all of their code and actively contributes several very important tools back into the scene (like ChoidujourNX, which lets you update firmware without burning fuses).
It's labeled a "starter pack" (due to trolls) but works beautifully. I highly recommend it.