It's an often argued point, but basically either will do the job - PIC has the advantage of much greater popularity, and much more support - but there's enough support for AVR as well.
Interesting comment from someone with "8051 specialist" in his signature
AVR isn't all that new, only when compared to PIC's (which it was blatently aimed at, even copying the PIC's three letter name), but hasn't really managed any great sales figures yet (compared to MicroChip).
But really either would do the job, or would even the 8051 (which seems popular out India way still?).
AVR, new??? That would make my 1994 Ford Explorer a new truck.
And with an 8051 background, I would pick the AVR as well.
If the OP is new and has no skills with microcontrollers, I would lean to the PIC for support (and this forum). Though the AVRfreak.com guys are very helpful as well.
Previous knowledge with 8051 has little to do with which microcontroller to pick for startup.
The PIC is a very good step forward for anyone wandering into the wonderful world of microcontrollers. I chose to start with the PIC although I am quite comfortable with 8051 and I'm still convinced that I have made the correct choice. If you trust me, you will encounter far fewer "difficulties" if you start with PIC other than AVR.
The best of all is the PIC will not lock you out from your own silly mistakes in MCU configuration. You can always recover from your mistake by reprogramming it. This one point alone is totally vital for beginners. Otherwise with AVR one have to use a parallel high voltage programmer that requires upto 20 connections to the AVR to resurrect the wrongly programmed AVR.
After one is comfortable with PIC one can explore the more joyful world of AVR and ARM.
Ahh! The default code protect checked on. That was way back for me. I locked a couple chips before I saw that was default. The 1200A (2313 with NO RAM other than the registers). I did not mind using the registers for my RAM. But wasted a couple chips.
That is not what killed Atmel/AVR for me. And they have a great product. I have a dragon programmer I might use one day.
I left them when I needed tech support on a Tiny11 project (that was a real winner for them I am sure) and I could not get the STK-500 to program it. Tech support was over a month later when they called and I had moved it to the Microchip (PIC). In fact go back in this forum years ago and you will see where I used Nigel's website and moved it to a 12F675
Umar,
The PIC is harder, but you have a lot of people that will help you. Also, what are you switching from?