Blockchain is a database. Bitcoin is a blockchain database with an cryptographic identity layer where transactions are mostly immutable. If all of the people who run Bitcoin don’t all agree on governance then the database is formed into two versions where the transactions before the fork are kept but after the fork the second group will have a different set of transactions (like bitcoin gold) . Ethereum has a super set of features which adds the ability to run a stored procedure which enforce a contract that will be run on the network but have the resources of a microcontroller .

Since the hello world of your own cryptocurrency can be done on ethereum it makes it popular in that respect. Stablecoins are coins pinned to currency values because of the volatility of the underlying coin poses unique issues due to people paying each other in bitcoin or any altcoin.

Bitcoin is the most mature implementation of a blockchain due to being in existence longer . Ethereum has had unique security challenges and transaction issues but since databases are hard to make correctly it will win out due to age .

Bitcoin has proven itself to be able to support speculative investment and faster transaction times than a SWIFT transfer . Ethereum has been used to implement altcoins and stable coins and also encompasses bitcoins feature set too).