Most people here prefer 8051 variants because most of their experience is with them. Also 8051 has been in the market for a long time which made it industry standard.
I prefer PICs because most of my experience was with pics and u get free development tools.
PICs have a built in power reset circuit unlike 8052 variants which u need to add external one increasing cost and board space.
PICs have higher current drive capability per pin 20mA source and 25mA sink.
PICs are RISC and single cycle instructions which make it faster than 8051.
PICs are abit more difficult to use and understand than 8051, but once you mastered them you don't want to change to any other processor if you want a single chip solution.
For most projects you don't need external ram and if you need to add it for some reason you select a PIC member that supports external ram.
Anyway if you need external ram its better to use a microprocessor and not a microcontroller.
I have development tools for both PICs and 8052. I can make any project work with either one especially if I write my code in C i can reuse it for any other platform.
Interrupts in 8051 family are far more superior to PICs but the speed superiority of pics compensates for this.
Internal architecture and addressing modes of the 8051 are superior to pics but who cares as long as your job is done.

Mahmood