Nearly all languages worth considering can compile to either GCC or LLVM one way or the other, the thing I find that makes the difference for microcontroller us

Nearly all languages worth considering can compile to either GCC or LLVM one way or the other, the thing I find that makes the difference for microcontroller use now is (to be worth using over C) the ability to abstract over the peripherals quickly (There is a project that I think parses the peripheral datasheet at compile time in D, even), preferably zero cost.