We tried both of them for one of the largest online classifieds and e-commerce platform. We started with ehcache/terracotta(server array) cause it’s well-known, backed by Terracotta and has bigger community support than hazelcast.
When we get it on production environment(distributed,beyond one node cluster) things changed, our backend architecture became really expensive so we decided to give hazelcast a chance.
Hazelcast is dead simple, it does what it says and performs really well without any configuration overhead.
Our caching layer is on top of hazelcast for more than a year, we are quite pleased with it.