Since I have not seen anyone mention, I have been using Blue Mountain calibration software for about five years or more. They have a new version that is really nice.
Strengths:Ability for custom reports through Crystal; ER/ES compliant; designed to be validated; can handle different events (calibration/maintenance/performance check); for a fee, Blue Mountain can merge existing data into the new database.
Weaknesses: Not sure; I am certain it has some, but I have not found any glaring deficiencies while using it. I am not that familar with other calibration software to provide a comparison. I did have one of the packages on a trial basis. The trial software had a fixed number of reports, with an additional fee for extra reports.
I have also taken one of the Access sample databases (that comes with Access) and developed a fairly decent calibration database. I had calibration reports, queries, cal due status, standards, etc.
I think it has already been mentioned, but some considerations are how many instruments you have, the level of complexity/diversity in your instruments, how many people will view the data, the level of users required, etc.