Different engine or an extra field?

Hi to everyone, could you help me with the correct way to proceed? I have a project in app search that is made up of 3 databases, all with a similar structutre, but each with a different source. So do I add one more field to each database where I indicate the source so I can filter by source? Or do I upload each database to a different Engine and then just do a Meta Engine and set each Engine as a filter?

Thanks