Loralee - it all depends on what you are looking for and how much detail is available in the service record. For genealogical purposes, most of the time the pension file will contain more information. However, if you are interested in exactly when he enlisted, when he was present for duty, hospitalized, AWOL, captured, imprisoned, etc. the CMSR is the way to go. Note: except in unusual circumstances, the CMSR will not show or prove his participation in a particular battle. Union records are usually more detailed and complete than Confederate. If you can briefly outline what you know about him, especially from the pension file, I would be happy to look at his CMSR and tell you if there is specific information there for which you might like to have documentation.