For people like myself who are really playing around with 3D printing it makes little difference. The change was made to leverage the extra power of a 32 bit system but it doesn’t mean 8 bit processor version will become obsolete.
The 32 bit processor offers some advantages. Like being able to fully run the latest Marlin 2.0.x software rather than Marlin 1.1.x. Evidently you can also <almost> run the later Marlin 2 software on 8 bit systems. But you have to turn some of the enhancements off and most reports say it is sluggish. So unless you’ve something that really demands it I’d stay with your 8 bit system (I will) running Marlin 1.1.x.
But how do you know if an Ender 3 has an 8 bit or 32 bit board?
Simple! Look at the USB connector. If it is a mini USB socket then it is 8 bit. If it is a micro USB socket it is 32 bit. So depending on which of these below plug into your Ender 3 then you can tell whether it is 32 bit or 8 bit.
The other way turn on the printer and look on the GUI display. Go to “About printer” and look at the version number
if it says 1.1.x – its 8 bit.
If it says 4.2.x its 32 bit