Clustering vs. transactional replication vs. availability groups

Question

Assuming you need to make sure your application that relies on SQL Server 2012 as its database backend is available around the clock, even if one server machine fails.

As a developer and not a DBA, I am struggling to understand when to use which scenario for my failover / high availability:

• Two (or more) servers in a Windows Failover cluster, SQL Server as a clustered instance
• Two (or more) SQL Server instances that are kept up to date with transactional replication
• Two (or more) SQL Servers in a SQL Server Availability Group, configured in a synchronous commit mode

Which of each of those scenarios works for what kind of workload, and what kind of failure / outage can be handled by those scenarios? Are they even comparable / exchangable?