Any alt coin suggestion expect ada.In my point of view of ada still can't surpass ETH in the smart contract field and even if they can make it will be hard to be replace existing eth smart contract eco system.Moreover late coming project like sol even surpassing to ada,all things ada have is the loyal user base and nothing special things in tech
I think ETH is the best investment. ETH is the best because it doesn't need to be sold because now there are a lot of places where it is applicable and in the future there will be even more such offers. In 2016 everyone moved dozens or even hundreds of ethers and it was not a lot of money. Ether is like oil that can be traded and it is convenient (in part it is).