There are honestly so many choices for a question like this. We can all guess and many will guess right and wrong. I see a lot of people mentioning some of the same ones I would also mention. BTC of course, however I'll go against the grain and NOT pick ETH. ADA, maybe EOS, ZIL, OMG, RHOC, KMD, TEZOS, XSPEC, VET, ENG are some of the ones I'm already in or interested in.