Which MacOS do you recommend?

Hey everyone.

I have a mid 2012 MacBook pro 13" I'm currently running Catalina but I'm looking to update it, due to a slot issue I can only use one port but I've upgraded it to a single 8gb stick of ram. I currently have a 500gb HDD but when funds allow I'm hoping to upgrade to a 500gb-1tb SDD.

What os would you recommend? Am I ok patching with it still using HDD?

Tia 😊