Ooty is a couple hills and a lake. Coorg is a big region, with many hills, coffee and spice estates and a lot more places to visit. Ooty is crowded, dusty and chaotic most time. Coorg is a quiet haven with not much crowds. You can decide as per your taste. https://www.tripoto.com/coorg/tour-packages
Both Ooty and Coorg are great places to visit.Ooty appears to be more geared toward mass tourism, whereas Coorg's highlights revolve around customizing your holiday theme and selecting destinations.