Otamendi is a strange one, he is probably a better defender than Mangala currently as would be expected. He seems too good not to be playing regularly, but playing him may stunt the Kompany-Mangala partnership growth.
From what I've seen so far Mangala is a beast at dealing with big guys, who we've played so far (Costa, Lukaku, Deeney) yet a bit less good at tricky players with more pace, which is where Otamendi seemingly shines (e.g. dealing with Messi so well for Valencia).
Interested to see how he is utilised though am excited to see him play for us. Hope he gets his paperwork done before the Palace game when the fixtures begin piling up.