I concur. Nano is one of the fastest cryptocurrencies I've ever experienced, as transactions settle instantly. It's based on the same DAG algorithm of IOTA, and it's better suited for micropayments or quick day trades. If this cryptocurrency adds smart contract capabilities, then it would be even better as it could rival Ethereum, EOS, Cardano and other leading smart contract platforms in the market today. Considering the bear market that crypto has experienced since the beginning of the year, I'd say that Nano is quite cheap to buy these days.
If it gains traction, then you could easily double or even triple your investment in no time. Another cryptocurrency that it's worth buying is Coti. While it's based on the same DAG algorithm as Nano and IOTA, this new cryptocurrency has a different approach as it aims to become the "PayPal" of the blockchain industry. It has a dedicated and professional team, which aims to become a global payment processor for the masses.
Lastly, there's Ethereum which has a lot of potential into becoming a widely adopted smart contract platform by businesses, companies, and average people in the real world. All it needs is to scale, to make decentralized applications viable again, and you'll see ETH prices hitting the roof. At nearly $300 per coin, it's quite a steal considering it's All-time-high of over $1,000 per coin last year.
All in all, do your own research and you'll see why these altcoins are the best ones to buy and hold for a very long time.