I prefer F#/F* syntax, but I had to go with Ada/SPARK2014 for the safety-related control systems I am trying to verify formally and use for high-integrity applications. Rust is making some inroads with AdaCore and Ferrous Systems partnering on providing formal verification tools for Rust like they do for Ada/SPARK2014, but Rust still doesn't have a published standard like C, Common Lisp, Prolog, Fortran, COBOL, etc. Plus the legacy is immense for Ada and SPARK2014.