mac book pro compatibility guide mid 2012

...now has original one.

Which OS version is that? It makes a difference on how we help you upgrade.

Be aware that, once you go beyond 10.14 Mojave, older apps like old version of Office and Adobe Creative Suite will stop working. I have kept my 13-inch, non-Retina Mid 2012 Macbook Pro at Mojave because it has an older version for Word that will open very old Word 4 through 6 files I have archived that are too old for newer Office versions to handle.

Before updating, check for apps the will ont be supported on 10.15 Catalina. This free tool will do so, and I believe it also checks to see if upgrades are available.

https://www.stclairsoft.com/Go64/index.html

As I suspect you also have the non-Retina 2012 model, it was the last Macbook Pro where the user coudl open it and ungrade RAM. Most shipped with 4GB RAM; for newer OS versions like 10.14 and 10.15, 8GB is better. If you buy from Crucial or OWC, you can achieve 16GB RAM, but mine has 8GB and has never shown to be short of RAM.

If you have the original slow mech hard drive, newr OS version with be sluggish. I replaced the original hard drive with a modern solid-state drive and the performance improvement was stunning.

Older Mac OS versions are available here:

How to get old versions of macOS - Apple Support

...but please tell, us your current OS version first. If your current version is really old, you may need to do the upgrade in two steps.

Best is subjective. But from a security and features standpoint, the latter the better. Looks like Catalina 10.15.37 is the latest you can install.