Speaking to the media ahead of this weekend's league game, the Spanish manager refused to compare his players but stressed the goalkeeper's vital importance to the club.
Asked whether the goalkeeper was his best piece of business, Arteta said: "I don't know - he's been a tremendous signing, there is no question about that. Whether he is the best or not is just an opinion. It doesn't matter, we are so happy to have him. He has elevated the team to a different level and now we have to maintain that level."
Discussing the goalkeeper's mental strength through early high-pressure moments, Arteta added: "I think it's his mentality. David has tremendous quality but he has overcome a lot of difficulties and challenges to reach this point. It wasn't easy at the beginning, he had to dig in and prove himself. Now, he has the right to be one of the best."