hi. The difference between the two is not in terms of efficiency, but more to do with which one of the two suits your requirement.
Window AC requires a duct to install and is available with various tonnages. Whereas split AC requires no duct, looks more elegant, though it may require some amount of installation costs, depending on your supply of electricity. Spilt AC's also come with advanced filteration features which are desirable for health reasons. You can read the detailed Air Conditioner buying guide on Croma's website here : http://www.croma.com/air-conditioners-introduction
Split ACs are silent machines . You willl find them in many designs which is not an option for window one
Partialy depends on your room size and facing. If you have high walls then you can go for split as they are good in cooling entire room compare to window.(My exerperice) . Budget is also important factor. Here is the more detail if you like to see.
Both are good its depends on room size and availability of areas / space ( for the wire/ space for outdoor unit / wiring issue )
In totally split ac is more efficient compare than window ac.
1 Air throw is better than window ac
2.Low noise level
3.Split life is long as compare window
Check out these writings , if your looking for air conditioner.
PS: Your better off with split AC.
Read my article and detailed info about ACs
from my personal experince window ac is the best option to choose for better outcomes
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If you are looking exactly for best ac in Split Type AC category then here is a good reference for it.