It's hard to tell a priori. Modern C (as distinct from C++) and Fortran are comparably fast and which you use can be a personal choice unless local policy dictates otherwise. I'm surrounded by C colleagues but I prefer  that all my bugs be of the Fortran type if only because I can detect and swat them more easily. Fortran is simple to learn and you can quickly recode a C algorithm and see which is faster (for that algorithm only and assuming both codes are equally well written). Did you know that Fortran 2003 is interoperable with C?

Gerry