Datacleanse before or after appending tables or within same table?

I have five databases for my companies.  Each deals with a separate country/company.

Currently I Import the db from sqlserver one instance of SYSPRO with 5 db.

I am trying to speed things up a little.

So what is best?

Import each and do cleansing in each ===> then Append    OR

Import each without any cleanse and do all the cleaning up in the Appended table?

Currently I can View Native Query in the base imported tables right to the end of the query.

A third alternative is to write a longer single query bringing each db in, then Appending those within the same table using the technique mentioned by v-sihou-msft  here:  https://community.powerbi.com/t5/user/viewprofilepage/user-id/6969 .   I have trialled this on a much smaller table and it seems fine.  Great tip btw.

Before I embark on a major writing exercise, any tips on speed issues:

1.  Import each table, cleanse then Append all in another table;

2.  Import basic tables, Append all in another table, then perform cleansing in the new table;

3.  Import using v-sihou-msft method.