Dear Arif Deshmukh,
These both have their own merits and demerits. You can not limit one the Best. it depends on situation in which you require uC.
if You use PicBasic for programming you will find follwing advantages in PIC
1) RS-232 communictaion without level converter.
2) routines to communicate with I2C eeprom
3) commands to input/output frequency and so on
But if you want to use timers, or interrupts it is easy in AVR/51

Thanks
Best Regards
Muhammad SAjjad