dear, the thing is there is no definite answer. there are threads like this one on PW, read the comments for at least last 1 year and depending on your budget, usage, load shedding, then only you can decide.
what i have understood that:
1. first ascertain what are your needs i.e. budget, usage, AC to room size, load shedding / voltage scenario, ambient temp of your city etc.
2. products and after sales availability: it matters if you are living in small city. urban areas do not face such issues. but after sales is anyways not up to the marks for any brand. local brands have some.
3. cooling and saving takriban same hai, one can vouch for a brand or model but no one has used all models and brands to categorize the cooling and saving. anyways, this is also a subjective thing.
4. and for model selection, i try to go for the one that has got good reviews regardless of the brand unless you are going for higher end brands. there may not be many reviews about higher end brands models.
5. installation: if your city or area has got no good installers, then which ever brand or model you buy, it may not perform to its optimum level or might fail to perform to satisfaction and thus this way many brands n models get bad name.
So, if you have already decided to go for any of above mentioned brands, then go for anyone, what your gut says.