MPLAB C18 v3.47: The Definitive Guide to the Final PIC18 Legacy Compiler
If you are starting a , skip C18 v3.47 and use the latest MPLAB XC8 with MPLAB X IDE . If you are maintaining an old project that specifically requires C18, v3.47 is indeed the "best" version to have because it contains the final set of bug fixes and the most complete device header files for that era. Using the MPLAB® XC8 Compiler - Microchip Developer Help
Industrial control loops (motor control, PID regulators) compiled with XC8 might shift their timing due to the compiler's aggressive new optimizations. C18 v3.47 is "dumb" in a reliable way—its assembly output is highly predictable. This is non-negotiable for safety-critical legacy systems.