I actually think Chelsea could flop this year. All they've done is sign attacking midfield players, and not improved other parts of their team that really need it, namely defence and defensive midfield positions. Plus what if Torres gets injured? Sturridge is really their only other central attacking option so they're a little short up there.
Add onto that the fact that RDM is now a hugely over-rated manager (though I'm actually a fan of him) who got fortunate to win the CL, and did so by playing very negative tactics, and you have more problems. Why? Because Roman won't be allowing him to continue this sit on the 18 yard box style of football, especially with the players they've signed. He'll want free, expansive attacking football which won't happen overnight so I could them struggling, especially initially.
For me, it's still going to come down to City and United. City have the better starting XI but United have a better squad depth in most areas so injuries could play a part. You take Kompany and Yaya out of City's team and they struggle, you take Nemanja and Carrick out of United's team and they seem to still grind results out.