Ultimately the choice of cluster stack is a personal decision that must be made in the context of you or your company's needs and strategic direction. Pacemaker currently functions equally well with both stacks.
Here are some factors that may influence the decision
SUSE/Novell, Red Hat and Oracle are all putting their collective weight behind the Corosync cluster stack.
Corosync is an OSI Certified implementation of an industry standard (the Service Availability Forum Application Interface Specification).
Using Corosync gives your applications access to the following additional cluster services
checkpoint service
distributed locking service
extended virtual synchrony service
cluster closed process group service
It is likely that Pacemaker, at some point in the future, will make use of some of these additional services not provided by Heartbeat
To date, Pacemaker has received less real-world testing on Corosync than it has on Heartbeat.
