Eagles are much more superior in every way.
-Their higher toughness will see them survive much longer.
-The relative low cost (50pts) makes them expendable and give you more points to spend on an already high cost army.
-Movement 20″ and flying means you can ignore most obstacles in any table of terrain or massed battlefield.

I personally will only field a unit of reavers if I’m playing a diversionary game alongside 2 Great Eagles. When you play a non combat army you won’t be winning big. The best you’ll do is middle of the table at a tournament which is great for some but not everybody.