Actually, even if speed is your only consideration you are still likely to be better off using C rather than assembler where possible. A decent compiler can generate better-optimized code from C source than all but the best assembler programmers could write by hand.
That is not to say that there are no other relevant considerations, but other languages are not necessarily any safer or easier to develop in than C; it varies depending on the project. Sometimes there really is no other viable alternative. For example, the only other realistic systems programming language I know of is D, which (while otherwise a great language) is not as portable as C (yet), nor nearly as well established so far as libraries and tool support are concerned.