I've long been an advocate of 4-2-3-1 with 2 pacey wide wingers & your most creative player in behind the striker when you're at home or playing a team you expect to be dominant against (most matches for City).
For tough away matches, or European football, I've always been a fan of having 3 big guys in midfield to solidify the defence & dominate the midfield.
So for City specifically, last season when we made the switch to 4-2-3-1 I was delighted, I still felt we were missing a pacey winger, which we've now rectified with Sterling. This also meant Fernandinho got more protection from Yaya as Silva was ahead of him (finally central) stopping him getting too far forward, & Sergio got to play up top on his own where he performs better. After the first few games it was clear out of the front 4 Navas was just not quite good enough at the top level - for me Pedro was the perfect replacement, like-for-like but more end product - but we've got KDB now. The worry with KDB is that he ends up having the same results as the Silva-Nasri combo but we will see.
So for Europe, last season when we bought Fernando I thought we were finally going to see it, Fernando deep in front of defence with Dinho & Yaya ahead, a strong midfield with protection to the defence - yet we played 4-4-2. I still feel we should try this combo out in Europe & away at title rivals, if we need goals we can bring on game changers but there's nothing wrong with starting the game off more sensibly & Yaya would have more freedom to get up & cause damage. Not convinced we'll ever really see this under Pellegrini but just my opinions.
Why I don't think we can play 4-4-2: well, simply everyone ends up out of position. Silva starts up out wide, then comes central, which means there's no width, which leads to a striker going out wide. Yaya has so much space ahead, he just jogs into it & has never been one to get back, meaning Nando/Dinho have to do the job of 2-3 people & every team we play with 1 pass gets through our entire midfield. On top of that the Dzeko/Aguero partnership was a poor one, how often did they combine to score? Negredo formed a great partnership with Aguero, & Bony probably could do similar - but again not worth forcing all other players out of their natural position.
Specific things I don't think we can do:
• Nasri/Silva combo, too slow, too narrow & too easy to defend against. One or the other should be on the pitch (sorry Nasri).
• Nasri/Silva/KDB combo, was very surprised Pellegrini tried this out against Juve, who exactly were these great passers supposed to be passing to? None of them make runs behind. Simply do not need 3 AM's on the pitch together it's horrible.
KDB has played RW a fair chunk of his career so the hope is he plays the position more like a winger & less like Nasri - time will tell whether this works for us or not. Hopefully see the Sterling-Silva-KDB combo against West Ham so we see what happens.