Even though ETH is already quite popular and has already substantial market exposure, I still think it's the best long-term investment. The concept just encompasses anything that can be encompassed, it's a programable Bitcoin essentially. The fact that is already has such a wide adoption (and so quickly) means that it's well received by developers and there are already many projects building on it. It's like Microsoft in the old days, they made Windows accessible to everyone and everyone still uses it up this day (the majority at least). The same is with Ethereum, developers are building on the ERC20 standard, and applications (which will be accessed by consumers) will be used by them, that's quite big and I think people have not realized the future implications of this.