i also do agree with that,
at some places you have to even take considerations of availability, for instance i being in Oman cant get micros easily and when i have to buy some i do it usually on my trip to Dubai... but even then i can just get PIcs there in local stores, hence for a single avr i have to pay the shipping costs as i have to buy it from online distributors...
so i do use PIC then...
at the end.... i would say that
you have to take lots of things in consideration, including your design requirements, availability of the micro itself , availability of resources for that design , etc etc...
one would be able to tell the best MCU for a specific design and other factors given... As a general its not possible...
even sometimes you have to chose one based on your skills with that MCU...