C-3PO was good in TPM, but he was annoying in AOTC, and not in the way he is supposed to be annoying in-story for our amusement. He was hardly featured in RoTS to be considered good or bad.
I could actually do with a SW film with a new droid character, on the good guys side, one who might actually pick up a blaster in a fight, but y'know, isn't supposed to, as in, isn't a battle droid.
It would be interesting to have a droid who gets involved in the fighting and ends up being treated like one of the crew as a result, hell, it would be great to see one who wished he was a Jedi, and secretly trained himself with a lightsabre.
In fact, there are a lot of possibilities for creating AI characters in the SW universe, they have been so used to C3-PO and R2 dominating that scene that they should maybe think of giving us something new.
What they need to avoid is a Jar Jar Binks type droid, what they need is Han Solo born into a droid's body, that type of character, a droid who pushes past his programming as he feels drawn to the adventure. That could be interesting.
They need to bust these movies wide open and expand the universe, some R2 and C3-PO would be good, but it might be the best idea to go for completely new characters and build them from the ground up, good characters this time, well thought out character arcs, not just there to amuse the younger audience.