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From energy efficiency perspective there is no preferred choice. Both split and window can be equally efficient.
Higher the EER of air conditioner higher the star rating it will have. So a 5 star rated air conditioner provides more cooling per watt of electricity used.
Both split and window can have high EER ratios. But it is observed that Split air conditioners have more number of models in BEE 5 star rating as compared to Window air conditioners. So if you are looking for high efficiency air conditioners then split air conditioners can provide you more options
Partialy depends on your room size and facing. If you have high walls then you can go for split ac 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.
You must check the 1.5 ton inverter ac, they save the best in electricity bill.
That entire depends on your requirements.
Based on your requirements, Best Green AC will tell you about which AC you should buy in India. Also, it has the list of best ACs in India that you can explore.