Signing the best player and having the best window are 2 different things entirely.
I think United have made 2 very good signings in Young and Jones. I imagine De Gea will also turn out to be a good signing.
City have signed 2 great players in Aquero and Nasri, while holdign onto Tevez.
But with my rose tinted specs on I think Liverpool have had the best window. When you consider not being in the CL spots, the streamlining which has taken place has been nothing short of miraculous. While there will be doubts from some non-Liverpool fans over Adam (for £7m it's a no brainer) and Henderson (@ £13.5m certainly more of a risk), Enrique & Downing are 2 players who will greatly improve the team. While individually they may not be "Aquero", their partnership on the left and the benefits they bring to the team as a whole will be invaluable. Like Jones, Coates could turn out to be a star, and again for £7m not much of a risk. Bellamy replacing Ngog as 3rd/4th choice forward or winger is a huge step up too IMO.
The fact that Spurs haven't improved their team at all in an added bonus.