I do believe that sooner or later the coins that are fully anonymous/untraceable will have the success.
Monero is already big, but it's far from its potential.
Aeon is a worthy follower imho.
But really, there are a lot of good coins coins nowadays (along with 100x more shitcoins, I know), so you'll have to do some research on most coins people suggest in this kind of threads.
Yes I already have Monero in my list, together with Ethereum Classic. I have not done any exploration in Aeon, but I heard it has one developer only. That is not very reassuring in my opinion.
Everyone, what about Decred? I heard good things and market capitalization is still low.