There are three major world lists available. A Checklist, 5th edition. There is no such thing as the world listing of bird species. Therefore I think the best thing to do is to choose the listing you feel most comfortable with. As a matter of fact, I feel most comfortable with world lists like the one by Clements.
Lists differ greatly on number and sequence of families.
The Howard and Moore list is very much a traditional list. So is also the new Clements list. The Sibley and Monroe list was the first based on DNA research. Families are fewer and re-arranged.