Microcontrollers: Which is the best?

This question arises in many places: circuit design, physical dimensions, and cost, to name a few. For my case (or rather, opinion), here are the important criteria to check for:

• The volume of data going in and out
• Size constraints
• Environment of the embedded-system

A processor handling massive amounts of data per unit time requires more power both computationally and electrically, a faster clock (which also needs more electrical power), and, perhaps, ventilation for applications reaching very high clock rates. Size constraints will always depend where the embedded-system is meant to be placed. A system containing many components in a confined area requires more careful designing and construction. Environmental factors are among the most important: humidity, temperature, and electrical spikes, to name a few. Generally, processors packing more processing power are less forgiving in terms of environmental extremes.

Generally, those processors whose only task is to control equipment through commands issued by a more powerful processor are more rugged in build, since although they have to handle quite large volumes of command/response data, they are spared of the more complex computations such as PIDs that are common in industrial automation, since controlling equipment is their only task. A small program may be added to handle the case that the I/O controller be separated (i.e., the communications link severed) from its controlling station or computer; but that is little.