OZ only disadvantage is in mileage:
- No elite bonus (only matters if OP has status with UA/CO)
- Some cheap fares earn only 50% or 70% miles
But almost everything else on OZ >> UA.
OZ is a very nice airline (IMHO - best in *A). I would not even worry about E+ if you are on OZ's 777 or 747, because seat pitch is decent.