which photo library should i use on my mac?

It all depends on many things:

• Whether you wish to pay for the app
• Your level of experience with photo apps (or willingness to learn)
• The type of editing you wish to do - minimal edits or extensive edits
• etc, etc

I use the Photos app on my Mac for editing photos taken with the iPhone as it is easy to use, easy to learn, can handle live photos, Portrait lighting, etc

I also use Adobe Lightroom for photos taken in RAW on my SLR where I tend to do far more extensive editing and local edits.

Horses for courses really. There are many others out there, but I find the above 2 more than meet my needs.

That really depends on your needs. Your Mac is coming with Photos for Mac (Photos User Guide for Mac - Apple Support). It offers a basic database (Photos Library) to organise your photos and videos and a built-in Photo editor with many adjustments and filters. You can call third-party applications directly from Photos. Photos for Mac can sync your Photos between your Apple Devices and update the changes across all devices. It is comparable to iPhoto, which is no longer supported by Apple. If you need a professional application, a successor to Aperture, you will probably need a third-party application like Lightroom or Capture One.

I am using Photos as a DAM (supplemented by some Apple Scripts for batch changing metadata) and Luminar 4 and Aurora HDR 2019 for easier editing.