Fainga'a over TPN? This isn't womens' rugby.
Comparing the two, TPN has more wallabies caps but both have stood up in big tests and can be considered to have big match temperament.
Both have about the same super rugby caps, both are known for being physical, both have played with Robinson and Alexander (though TPN has also played with Ryan).
TPN is very prone to injury (I think it was Scott Allen who said on the podcast "When he tackles, you don't know who is going to get up") and while I'm not a sucker for the story that he can't through straight, he is not as reliable as Moore or Hanson.
Same story with Fainga'a for the throwing, but he is not at all injury prone. When he and Anthony played John I Dent, I remember them being called Search and Destroy. This has definitely transferred to the super and international stage.
Now that's the history, if we just look at current form, TPN has played two and a bit games this year and while not bad, wasn't overly great either. Fainga'a has played five games starting and two off the bench and has had two good weeks and the others were about the same as TPN.
Looking at all this is what leads me to say I'd want Fainga'a over TPN.