I have used 8051's for >20 years and PIC's for about 6 years in countless projects. My choice between the two, and likely yours too, will be based on requirements for functionality, price, sourcing, tools, etc., with the criteria being project-specific.

I am not an 8051 bigot or a PIC bigot (or Motorola, or...), just like I'm not an ASM bigot or a C bigot. Do your research and make your selections based on what best fits the requirements.

My observation is that PIC's seem to have a bit more peripheral functionality built into some of their low pin-count devices.

One possible downside to PIC's is that they are mostly single source.