Hi,
There is nothing like “the best microcontroller in the world”!!
8051 is the most basic microcontroller, it is easy and the best microcontroller for beginners to start with.
Once you have a feeling that you have done enough experiments with the 8051, then its time to move on to advanced microcontrollers.
Selecting a microcontroller depends on several factors, like
-Architecture(8bit or 16bit or more)
-Processor
-Peripherals(like uart, usb, timers etc.)
-Support available
-Cost
There are microcontrollers with few peripherals like 8051, and commonly used microcontrollers for application development like PIC16F877, ATMEGA8, ARM7, and highly industrial standard microcontrollers like RENESAS, FUGITSU and also microcontrollers which can be used as a complete sysytem (SoC) like ARM9, ARM11 etc.