Imo, it has to be one of Petr Cech, Hugo Lloris or Bernd Leno. Cech is the most well-rounded and best of those keepers imo, but the age (32) is obviously a factor. Lloris is a fantastic shot-stopper but is less convincing in the air. Leno has the most to improve, but he is tall and strong, a great shot-stopper, and young (23). He'd certainly seem to represent the best long-term option but there is the possibility that he may want to return to Germany and go to Bayern, similar to the case of David and Madrid. Cech would be the best option in the short-term imo, Leno would represent the best long-term investment if he doesn't decide to leave in a couple of seasons (that's a big if), and Lloris represents the middle ground. At 28, Lloris could potentially stay here longer than Leno, offering at least 5 years at a high level. His shot-stopping is probably top 3-5 in the world, however we may have a problem from corners with him as our defence tends to struggle with corners anyway. It should be considered that these Kane to United rumours are likely genuine and the price demand for Lloris will likely be overly expensive with 4 years left on his contract.
Imo, we should get Cech. He might seem more short-term than the others but in reality, he could end up staying just as long or longer than Leno. With only one year left on his contract and Chelsea's agreement to let him go, he would certainly be the cheapest option, especially cheaper than Lloris. He's also still one of the top 5 keepers in the world imo, and there's no reason that he won't have a long keeper career. While it might seem we'll only see the best of him for 2 years max, that could well be stretched to a period of 4-5 years (van der Saar is an example of this).