The utility of + frames is the strongest part of EX stealth. It's much easier to actually apply without specific setups, and makes a huge portion of Reptile's options either safe or advantage on block. It lets Reptile safely convert from one of his best normals (f2) and invisibility is fucked up in that you can't space the character properly anymore, and the invisibility creates a silly mind game that baits out some major mistakes.
EX basilisk is really good when it's active, but that's part of the issue. Getting it active. Though, I think the buffs to it in the beta will open up some pretty significant opportunities.
I think in the long run, they'll be interchangeable. If you're playing vs a character who doesn't blow through a majority of Nimble armor breaks and isn't so difficult to handle in the neutral due to whatever reason, I'm gonna be picking up Nimble for that (Quan strikes me as the most susceptible to Nimble). Vs characters that do one or the other (like Lao), I'll use Deceptive. I've only really found one matchup where I could really use Noxious, and that's Jax, just because he does both well plus he's super aggro as a character.