Best Solution to create audit/change logs

The setup for your audit logs can be whatever you want depending on your use case. If you only care about auditing a single field then you only need the current/prev value for that field. 

If you want one massive audit log where you log ALL fields that you want tracked into a single record, then you'll need a field for each current/old pairing of fields. 

I choose the approach of treating each field like it's own audit record - more similar to how QB does their actual internal audit logs. I do this by having a condition for each field in my pipeline that compares the current and old value. If they're different then I put that entry into a bulk upsert for audit changes and load it. So if my record has 20 fields - but only 2 changed - I only create 2 audit entries for those two fields. My audit table only has 5 main fields, new value, old value, who changed it, when it was changed and the parent record it relates back to.