Hi,
For PIC, people usually start with 16F84A, which has only a TMR0 module and no ADC/Comparator/SPI/UART module, but is used only to start off with PICs. Then you can move to 16F877A or better yet, 18F series and then to PIC24F.
Just out of curiosity, why are you deciding to come to PIC from 8051. Atmel has ATmega series of microcontrollers, which, when programming, I found much better than PICs. And if you already know 8051, it's going to be very easy to program ATmegas. Moreover, they're very cheap.