FHIR is the latest standard by HL7 to exchange healthcare data between disparate systems. It uses modern web-based technique Rest to exchange data. FHIR has bridged the gap of interoperability by providing mechanism to exchange data over the web. It is widely getting accepted for interoperability standards across globe and indeed future of interoperability.
HL7 V2 new
HL7 V2.x is the oldest and most used messaging standard by HL7. Most of the healthcare systems within hospital uses V2 messaging to exchange data in real time. Probably, more than 80% of interfaces are designed using V2 messaging as of now.
RIM+ CDA + CCDA new
HL7 V3 and CDA are two of the HL7 messaging standard. Though, use of V3 for data exchange is not very popular but RIM (Reference Information Model) is quite a success. RIM is an abstract reference model which provides base to derive further models to support various interoperability scenarios. All V3 domains, CDA and SPL standard are derived from RIM. Purpose of CDA is to exchange clinical documents. CCDA documents are constrained version of CDA