The genuine greddy is a better unit for sure... by the time you port match, relieve the 'dimples' for the screws, have all the mating surfaces machined flat on a fake one, then you have spent more than a genuine one allready...
Saying that, I spent a few hours matching up my genuine manifold to the tb's and smoothing out the casting marks anyway.
...tbh, the main reason I wen't with a greddy manifold was because it's 2 pc and I can ballance the tb's more easily (and it has hand flat boss's to mount all my N20 nozzles on he he he).
J.