The P&W PT6 family of light turboprops have been around for long and it's derivatives are still the most trusted turboprops in the air.
The Allison series improved well over time, but some of their negative traits have never been ironed out.
The phenomenal success of single turboprops, especially in the executive and medical role (like the PC-12 and Cessna Caravan) are singularly because of this family of engines