Better is subjective, but there’s a few differences between them that make it appealing to see Ether as “better” than Bitcoin.

There’s a few differences:

Bitcoin has a hard issue limit of 14million coins
Ethereum is “active” with decentralised applications using it to execute tasks / smart contracts. Bitcoin is “passive” and cannot work in the same way.
Bitcoin is mostly just a currency - Ether is a currency that is used within dapps.
It’s this use as an automated system that makes Ether appear better than Bitcoin, as it is embedded in a network of useful transactions.

This utility therefore future-proofs it a bit more in some people’s eyes, and makes it “better”.

Eventually Ethererum is planning to move to a system which is based on earned volume - so the more stakes a user has in the network the more Ether they receive as a reward. Bitcoin’s criticism is that it focuses on hardware mining that wastes computational power. By rewarding higher stakes, again Ethereum is more tied to utility.