Ethereum is beside BTC my favourite coin till so far. The future of most altcoins are uncertain, but
Ethereum is proven itself to be a solid coin with mass volume.
If you say Ethereum is next to BTC, it looks like they are both like kings and queens,
if I think it is more appropriate to say Ethereum is just below the BTC, it means that there is no other Altcoin that is able to be second at this time according to volume demand and trade volume.
A few years back the Queen of bitcoin was Litecoin in terms of both trade volume and demand, but due to the benefits of smart contract deployment on the ethereum blockchain it took the crown from litecoin in a short period of time when developers realized the true money making power of the smart contracts and how they can be used to make ICO and run many different projects in just a few lines of code. I personally like Monero due to its privacy features which are second to no other coin in the entire market.