Bidirectional data transfer
Distributing reads is easy; distributing writes is not. In SQL Server, most availability technologies require a specific node or database to be the "master" where all writes go.  Some possible options:


Merge Replication
Peer-to-Peer Replication
Transactional Replication with Updatable Subscribers (deprecated)


What is "best"? That's not really the kind of question we can answer here unless you get much, much more specific about what you mean by "best."