C++ and AVR-GCC.
There is free a C compiler for PIC18 but it doesn't do any sort of optimisation and it is very strict in how it likes you to write code - if you want a compiler which optimises the code you have to pay Microchip many hundreds of pounds. The one thing I have found when working with PICs is that there software is so intermittent in whether or not it works.
The AVR also has better (well more useful) hardware timers (PWM, counters, interrupts etc).