But the popularity is beginning to fade when there is a new generation of blockchain like Cardano and EOS and both coins both have the chance to become the next popular coin although it can not beat the dominance of bitcoin.
i think that nobody know the answer to you question because how would we know , and i guess that if they knew , they would not tell because they are going to be rich , but if i had to say 1 i would say NEO
Since we know how popular EOS on the altcoin.
And also EOS is built on the backbone of the Delegated Proof of Stake (DPOS) make Eos different from the others