Multi-master replication is rarely a good idea. You will get data collisions unless you rigorously partition the workload. Conflict detection and resolution is not adequate to guarantee consistency over time. Recovery back to a consistent state after a failure is complex and error prone. I'd strongly advise against a multi-master setup, especially for a high volume system.
You seem to be concerned that 2 out of the 3 systems may fail resulting in a site outage. The likelihood of that is small if you have set things up with separate power etc. With the A/S pair based approach you would still have query capability if the two master systems failed. The chances of all 3 systems failing is not that much less than of just 2 failing in reality I would say (depending on the reason for the failure).