Nani is good, he is World Class on his day and probably would suit better in a 4-3-3 than in a 4-4-2, he wouldn't need to move back that much. He may be injury prone but he has only got 1 more injury than Cerci since 07/08 so that shouldn't be a factor.
I'm really intrigued about Conte wanting Nani so much, was all the interest real or is just the media linking him with us? If Conte reaaaally wants him and the price is right (€13-17M) I'd say give it to him. Who am I to question someone like him.
The biggest thing I don't like about him is that he is really inconsistent. One day he's unstoppable, creates danger from every corner, pulls any trick. And the next one he's shit. I wonder if Conte and the right motivation could fix this. He needs a change of scenery that's for sure. Look at what Tévez has done for us, Nani could be something like that.
And I also feel he's kind of selfish, and that he is all about flair and very little ending product.
Cerci won't be anything outstanding. We know what he can offer, pace, a good left foot, along with the possibility to use him as a SS (I feel that he will end up adding the same as Giovinco this way) and almost nothing else.
Nani could end up being great for us if everything goes well, and if it's for almost the same price I'd go with Nani. It's a gamble.