What about libfmt? Frankly I find it a little easier to use than double-conversion and it's equal in speed.
Internally it uses the same algorithm, Grisu, (with some additional optimizations) so there shouldn't be any difference in output.
If it's easier to use for you, just go with it!
I'm guessing the double-conversion library is a bit more flexible, but I could be wrong.
#include "third_party/double-conversion/double-conversion/double-conversion.h"> Expands to the most recent, preceding word for which this is a prefix.