The subject says everything. What is the difference of arduino uno and pic18F4550? in what ways does arduino uno is better than pic18f4550 microcontroller?
The AVR also has better (well more useful) hardware timers (PWM, counters, interrupts etc).
I wonder - does the Arduino/avr compiler do optimizations?
I'm sticking to Arduino/AVR, if you outgrow the Arduino IDE you can always use your favourite editor and use gcc-avr to compile your programs.
I believe the Microchip C compilers are also based upon GCC,