I and most people I know would recommend Linux if you're really concerned about security, however, Memory said it best with "the security of the OS depends on the user who is controling it ...the OS is not secure by itself ". Really, you should go with whatever you are most comfortable with using and then secure it to the best of your abilities with all the things Memory just listed. About "not prone to crash": Linux is nowhere near as prone to crashing as Windows (in my opinion).
-keezel