Created: 2020.06.16
How I am deciding between these different platforms on a project by project basis. It started when I asked the question of myself: since the Arduino is so much more expensive than a comparable Raspberry Pi Zero or Zero W, why would I not always use a Raspberry Pi Zero instead of an Arduino?
One thing I've noticed through the years. Is is a common thing for politicians, 'popular' scientists and pose the question in the form of stating a 'fact'. Note that I asked myself a question that made the claim that an Arduino is more expensive than a Raspberry Pi zero. But just because I, or a politician or a so called scientist trying to get you to believe a political viewpoint, makes a statement in the question, does NOT make it a fact! Indeed, the question itself is often a lie.
So lets start with a more honest question.
Arduino boards are copyleft, so you can get lower cost boards than the Arduino 'official' source. So the cost does not have to be as high as the 'official' board. They have decided that they make more money competing as 'the official' version and charging more, they leave the really low price competing to the Chinese versions.
The Raspberry pi is not as open source as it first appears, I'm told that Broadcom has some bits in the processor that make it impossible to create an identical clone to the Pi.
The Raspberry pi Zero is not as low cost as it seems, you need to add a MicroSD card to do anything - and that means that the cheapest pi Zero is about the same price as the cheapest 'official' Arduino, and definitely more expensive than some Chinese so called 'clones' or 'knockoffs' (depending on how insulting the person wants to be about them) of the Arduino. A quick check (2020.06) on Aliexpress yielded a $4.12 with free shipping to Canada for a Nano V3.0 compatible clone.
So right off the bat - the Arduino is either the same price or cheaper than the Raspberry pi. This means that we need to look at other factors to decide, project for project, which is the better choice. #When to choose Arduino, Raspberry Pi, Raspberry Pi Zero, Raspberry Pi Zero W The Arduino can run with substantially less power than the Raspberry pi. Some applications allow it to run for a year on a so called 'coin' battery. A Raspberry Pi Zero in the lowest energy mode doesn't come even close to that little power.
Want a low cost, albeit slow, desktop computer for web surfing and more? No choice, you need the Raspberry pi, and you probably want a pi 4 with at least 4GB of memory, even though yes, that is more expensive than the Pi Zero.
Want a laptop? Same thing. Circa 2020.06 for about $300 US from Adafruit you can buy a shell with battery, kb and screen to put your Raspberry Pi 4 into, I've seen at least one other option as well.
Need a device to power up quickly and get to task after a power failure? You need an Arduino. The pi is going to take about 30 seconds if you are running Raspberry operating system. Note I'm told you CAN run a Raspberry without an OS with quicker boot times, but this is definitely not something there is a lot of info about. It is not the way the community uses them. So even though you CAN do this, based on where the community is circa 2020, it makes more sense to use an Arduino. Note that most of the good stuff that comes with using an OS goes away as far as I can tell if you run it the pi without an OS, so it just makes sense to me to use an Arduino if I'm going to go through that hassle - that way I can lean on the work others have done.
New a device that won't get corrupted when a power failure happens? You need an Arduino.
Have an IoT function? All three can do the job, so this is a 'depends on other factors'.
Need Windows? You need a Raspberry pi. Note this is a basic bones Windows for IoT more akin to a Windows server running in command line, not a full 'windowed' version. You won't want a Laptop Windows pi.
Who has the most and most varied sample code? More or less a tie. It will depend what you need.
Talking to the internet. This removes the Pi Zero from the list - you would clearly go with the pi Zero W if you want this or of course the other Raspberry Pi models. The Arduino standard I'm told doesn't make this easy either - but you can buy addons or you can buy boards that have WiFi built in. So, while years ago this was a deciding factor, it doesn't seem to me to be a factor to decide between platforms anymore, just between specific devices in the platform.