Comparison: PIC - ARM - AVR

And what about the difficulty of migrating to (let's say) a 32 bit microcontroller when you have started with one that's 8 or 16?

Anyways, thanks a lot for the help you have already provided.

No its not difficult, the only thing required is to understand the new architecture. Migrating C code from 8 to 16 or 32 is not difficult but if there is architecture specific changes need to be done then you may have to workout.

So its always better to keep your application and low level layers separate to make migration easier.